Aperture and T-stop are a little different. Sometimes very different. Losing 1T stop is not unheard of, and you will see the
best case scenario only dead in the centre with periphery up to 2-4 stops behind, and even more if you buy some fancy new Canon RF glass
.
Lens corrections, which I guess are not available for PEARgear, can make a big difference too; so you want to compare with everything off. In worst case sony drops a wrong profile on in camera. You really don't want that at all.
It is a cheap lens and aside from complex measurements i
t still allows you to do reasonable work, as you said it yourself. I expect I would have more to say about it, but you never know. I am not keen on MF only lenses for my work, unless they are so wide that it no longer matters (i.e. 17mm or wider).
However I absolutely don't see a single reasonable reason not to use your 1.2 lens or AF 1.8 lens instead. None whatsoever, other than making some statement.
Now in the case of that samyang 14/2.8 it worked one year, and next year I picked it from the shelf it no longer did and I could not reassemble it, comprising a
100% loss of function. I could only hope their recent AF lenses got their act together. As long as I can get a reasonable end result I didn't care much about T stop; it was clearly very bad but came in at a fraction of cost of a rather shoddy and very expensive EF 14mm f2.8 prime (i.e. ~20% cost). It sort of ticked that box while it worked. I took maybe 30-50 shots that I kept (usually the numbers are in tens of thousands for my average mainstay lens). It was just way too wide for anything other than tiny toilets, and these just didn't deserve a lens swap. Distortion and vignette was CANON-RF level crazy
and focus scale was completely off. It was a really mega shoddy lens, but it was acceptably sharp on 20MP sensor until it just decomposed to complete trash
By the way anyone looking at 10mm FF lens you better realise how INSANELY wide it will be with all fisheye-like geometric and perspective distortions that will never ever correct to anything reasonable. 14mm is beyond usable for most work, and that comes from someone who uses 16mm lens for most of my commissioned work.