Having flown with a variety of tinted/non-tinted canopies, I would say that
on an average soaring day they seem to make very little difference to
vision and/or heating. In very low light levels (twilight/dark) I'd
prefer to be under a clear lid but practically it wouldn't make a huge
difference.

IMHO you're probably better off with a clear canopy + cover + a decent
pair of sunglasses: at least you can change/remove the sunglasses...

The "Perspex" normally used for glider canopies is transparent from
about 350nm and longer wavelengths, which includes part of the UVA band.
There is enough energy in the photons there to cause skin/tissue damage,
so although you might not visibly "burn" as much as in direct sunlight,
it's not at all good for you. I'm a bit sensitive in this respect so for
me high-factor sunblock is a must in a glider. You can get "UV 400"
Perspex which only lets in visible light but I've never heard of a canopy
being made with it (maybe I should ask!)