I'm not wildly impressed with the Tamron 500mm mirror, but the 350mm F5.6 seems pretty good and has quite a following.
I can't offer any particularly stunning examples as I've not really had chance to play about with mine yet. I managed to pick one up at a very decent price on ebay, knowing that if I advertised and described it better, I would be able to sell it at a profit if I don't get along with it.
I had a very quick try a few days ago; I'm sure both I and the lens could do much better with more practice, less wind and a bit of sunshine.
Collared Dove by
peak4, on Flickr
Poor lighting, so 1/320 @ ISO 1250, F5.6 of course as that's fixed, and fitted to an Olympus OM-D.
More or less out of camera, with a little bit of sharpening, as it was set to low on the body. AF is obviously manual only, but the Oly cameras will let you select the focal length for the In Body Image Stabilisation, which helps no end.
See what folks mean about the odd bokeh?
I gather both the Olympus and Minolta 500mm mirrors are worth having, but not for you, and the Russian Rubinar often gets a good writeup, though it is rather heavy.
The Minolta even has AF which is a bit of a rarity on mirror lenses; obviously that won't help a Canon user.
There's a whole selection of 3rd party mirrors available
second hand, but most will probably struggle to come up with decent resolution on a modern Digital SLR.
I certainly wouldn't buy new, but why not bide you time until one comes up with a suitable mount on ebay at well below average price. You can have some (frustrating) fun and then sell it on again without losing anything.