GreyLord
Legend
I played in a game run by a man who preferred 1st/2nd Ed., but who allowed 3rd ed in. It was a mess.
He was running a published module (3.5) that I'd been through before. I warned him of my foreknowledge, and kept mum about what I knew, but that foreknowledge gave me an insight to the things he wasn't seeing straight.
1st Ed gave movement in squares, not actual feet. Squares in 1st Ed were 10 feet, so the way this man ran it the place was immense. Iterative attacks in 1st Ed were different as well, and bows started at two shots per round. Mix that with a 3.5 Ranger with Rapid Shot and the DM was in shock at what was happening.
Without belaboring all the difference he ran into, let me simply say that it's the little difference that sneak up and bite you in the behind. Expect surprises.
That would have been easy to HR. You really want to take that feat? It's not going to give you any benefits...but you can take it if you want. (If I were running a game with 1e/2e rules but allowing 3e classes in...3e classes would have to adapt to 1e/2e mindset).
(and of course the vice versa of that, if I were running 3e but allowed 1e and 2e classes they'd have to adapt to 3e rules...though I think many of them could be underpowered in relation to 3e classes overall in that instance)