IMHO, the only thing that has really kept me from ordering a Foundation already is the weight/balance situation with them... After seeing and shooting a bunch of them, seems like every guy who has one has had to come up with a MacGuyver'd plan as far as weights are concerned. I don't know if I've even run into 2 guys who've ordered their weight kits from the same place? So I really wish Foundation would come up with a more standardized weight system.
I'm pretty much stuck on ordering 26" Proof prefits for the foreseeable future because they're cheap, good, and pretty beefy as-is, so I'd like to be able to easily balance and/or add weight to the rig using a barrel/contour that's more typical/ubiquitous like that. Seems most of the guys I've met who were happiest with their Foundations were rocking ~28" truck axles that definitely didn't just come off a shelf.
Depending on what you're doing, that's not to say it's a whole lot easier with Manners either these days though, I just received a TCS the other day, ordered the same exact spec as one I already had, and it showed up with the lighter 419 rail instead of the heavier steel rail. After talking with Tom, seems that the 419 rail far and away gets ordered most of the time, so I'm not sure Manners is going to even offer the heavier steel rails anymore (which sucks IMO because the 419 sawtooth rail stinks compared to the steel option, next to the steel rail the aluminum rail feels flimsy almost).