I’ve got a Propel, really nice bike but it is an aggressive position and ride and although it’s perfectly good for general riding it is more at home racing.
The TCR might be a better option if you are only racing occaisionally but it is a very different geometry, should be a lot more tolerable depending on how flexible you are.
I’ve had 2 TCR’s, one was about 10 years ago, I totally loved it, at first I put proper TT bars on and used it with a disc wheel and tri-spoke, and did my first sub 60 25MTT on it, still not gone much faster on a proper TT bike.
Then changed it to be a road bike but with clip-ons, did ADH tri on it and lots of miles with no problems. It then started aging.
I got another about 2 years ago and struggled to get on with it, I could feel my left leg having problems, but I think it was more likely to be me than the bike
Anyway, you can’t go wrong with a Giant really. If you aren’t racing that much I’d probably go with the TCR, if you do or can get away with a firmer ride and aggressive setup go with the Propel. Does he have any old ones you could test?
Finally, can you use cyclescheme from work, it will save you a fair bit of tax.