I bought an M42 to Nikon-F adaptor (with infinity correction element) when I bought the electric-picture-maker, so that I could try some of my old screw-fit lenses on it....
Ones that I have hung onto include; Pentacon 29, Zeiss 50, Hanimex 135, Pentacon 300, Panomar 12 'fish', Helios 44.. I did have a 70-180 zoom I never used knocking around some-where, and there were a few others. Also got a couple of teleadaptors; a 1.4x and a 3x I think cant remember what brands.
Panomar (re-branded Sigma), was one I wanted to be able to try, but rear element protrusion fouls the infinity correction element, so a no-go on that one.
Pentacon 300, was fitted up to get more reach before I bought an AF long lens. When I did, shots from the Pentacon immediately showed up how much modern AF lenses are compromised to keep costs down, especially so at the consumer end.
With 1.5x crop factor, the 29 offers close to a 'standard' FoV on the EPM, and f2.4 I think, without digging out the bag, makes for a bright view-finder and some nice shallow focus, whilst scales allow for easy selective focus, whilst shaming IQ of 'kit' lens. 50 & 135 are much the same.... and all are lovely lenses to use.... BUT!
Ultimately it's a cheap trick; the small sensor size of an APS-C electric-picture maker, is the weak-link; on a 4/3 sensor with even larger crop-factor, I can only see it being even more so. The Crop Factor, gives the FoV of a longer lens, but it doesn't change the DoF, so if that's what you like about them, then you at getting all they have to offer on a small sensor camera; you have to pull back and increase camera to subject distance to get the same framing, and that inherently increases DoF, defeating the usually 'fast' aperture; shorter lenses, that would let you get closer and reduce DoF for the same FoV and exploit the aperture, though are still suffering the Crop-Factor, and lenses much shorter than 20mm were never very available for manual focus film cameras..... so it's a cheap way to get a lot of easy-reach, and better IQ from an electric picture maker, but, you don't get all you could from your 'cheap' lens, while you get all the 'faff' of using a manual focus camera, and possibly a few more, using one on an adaptor that's not talking to the automation in the camera, along with it, potentially making them even more of a 'faff' to use. Biggest 'advantage' of an electric-picture-maker, to my mind, is simply it's 'convenience'... which an adapted lens is rather defeating..
So, conclusion, for me, has pretty much been to leave them on the camera's they were intended for, and chuck a roll of film in them!
I have an 'old' dedicated film scanner; cost me half a bludy grand sixteen years ago!!! .... picked up a
second hand one off e-bay last year for just £30! With modern scanning software, it delivers 10Mpix scans, at 48bit colour depth, as good as anything you would have got straight out of an Electric-Picture-Maker, until probably five years ago, and still as good or better than most in the amateur arena, and with "Full-Frame" FoV/DoF properties..... I DO get all those lenses could offer... and it's barely any more 'faff' to get'em! All the family-photo's I took, util I bought my electric-picture-maker, four years ago were taken on manual focus 35mm film cameras... for convenience I grabbed a compact, and accepted the lesser image quality; for 'better' shots I grabbed one of the SLR's and accepted the small added 'faff'. In that, I dont see that much has changed; Widgetal for convenience, & accept the lesser quality, or film for 'full-frame' better and accept the faff.
So, if you are really concerned with 'better' photo's, then you don't pick a small format/sensor camera as your start-point....
If I had stumped up for a full-frame DSLR, then I suspect that would start to show just where these 'cheaper' old '3rd party' MF lenses aren't so wonderful, but then a modern Full Frame Digi-Nikon will still mount most, old F-Mount Nikkor lenses, that are probably optically as good optically as modern AF offerings, and usually a lot cheaper, if perhaps still far from 'cheap'; but the big sensor has removed the weak link.
Mounting legacy lenses on smaller sensor digitals, is muddling in the middle of the compromises, then, and unlikely to ever deliver the best of both worlds you might hope, while any 'gain' you get will be at a loss, and probably a larger-one elsewhere in the mix. You aren't ever going to get 'Full-Frame' or Medium-Format like perspective from a small sensor camera, even if you can get a 'acceptable' image quality, you wont get the same framing, perspective or DoF effects. Using a Manual Lens on one, then, instantly removes the 'convenience' of a Auto-Focus lens designed to be mounted to it, before you find any other niggles to convenience, and whilst you may see an improved IQ from only taking a image from the sweet-spot in the centre of the 'cheap' legacy lens, if that is so important to you, then it's a bit of a blind alley to get it; It's a hint at how much more you could have, but it's not the full story. Full-Story is you are asking more of the camera/lens you have, than it is really able to offer; and if you really want to step up to that level of image quality, its back round the loop, to look at the sensor size, and stepping up the grades, rather than trying to stretch the margins a little.. and then, the £20 spent on the 'cheap' legacy-lens, isn't, it's £20 that could have gone into that better and 'matched' camera/lens you upgrade to, so it is probably not even a 'cheap' way to slightly stretch the boundaries very much.
But, yeah.. they ARE great fun to play with... and if you are enjoying that, then my advice would be to get the 'most' fun from them..... buy a roll of film or three, use'em as intended!
Notion of buying an old Olympus OM10 & Zuiko 50/1.8 for a tenner, or a Zenit and Helios 44 for a fiver, and chucking away the camera, to mount the lens on a small sensor digital, is to my mind something of an anathema! You get the full faff experience using a manual focus film camera with a manual focus lens, and you have the opportunity for even MORE faffing-fun, getting yourself a dev-tank and kitchen-sink 'souping' the negs... even colour developing isn't all that difficult, or require any huge amount of space or equipment, and THEN you have the faff-fun of scanning the negs, into the widgetal-world, opening up all the faffability you have for photo-shopping your images, as you do with an direct from camera electric picture... just be warned that its a slippery slope, and leap from 35mm to Medium-Format..... but still
Costs a quid for a roll of Agfa Vista from Poudland; costs £3 for a Dev& Scan at ASDA... that's a lot of full-frame loverlyness to be had for pocket-money prices, and you'd have to take a lot of photo's before it really did cost 'more' than buying a supposedly 'free to run' diigital...... it's got to be worth a thought, no?