There wouldn't be exp penalty because they'd all be within 1 of eachother. And I'm just pulling feats from the player's handbook and off the top of my head, so don't bug me about whether the feats are underpowered. Quite frankly, these are extra feats that a fighter 6 wouldn't have. In any case, even if it's just a slight advantage in what a player can do, it's enough of an advantage.
We're always arguing what's broken or not as compared to a wizard, well I don't mind that wizards are insanely strong. I can kill a wizard at any time I like. Oh no, she wasted a great deal of her precious exp and money to gain blinking and invisibility? Her hit points, AC, and fortitude still suck and plenty of my monsters don't care if you're invisible or if they miss a few times. It's when those tanks start holding their own that I get worried. Granted, I could run every encounter as if the fighters aren't their and just wail upon the wizards, but I don't. When players build their characters to withstand damage, I don't punish them for it by never letting monsters try to strike them. I build my encounters around my players. It's only when any given player could clearly survive on her own with a cleric cohort that I believe it's unbalanced.