Based on the amount of money you spent on them, I can almost guarantee you will feel something whether you feel something or not, that's human nature. While it is better than stock, it's not what it could be, or should be. Tubular steel is tubular steel, but its diameter, wall thickness, composition, shape, and most importantly...what areas of the chassis it ties together...can be very different.
The two real times I have seen significant differences displayed in subframes (stock, standard, full, bolt-in, and through-floor) are:
1. when jacking the vehicle up
2. on the road course, especially on turn-in after extremely long braking periods
Being that most don't do enough of #2 to feel the difference (my best description would be a feeling of disconnect between initial steering input and turn-in), jacking up the car is obvious. Lift a Fox-4 chassis by either the rear driver or passenger side on the torque box. A stock car and bolt ins or standard lengths will allow a disturbing amount of gap between the tire and the ground before lifting any other corner. Many cars will not lift the front wheel at any point. Full lengths will lift the opposing rear tire much sooner, and very well installed ones will lift the front wheel at some point. Through-floors will lift both the opposing rear and the front very soon, if not at the same time as, the tire nearest the jack point. At the extreme end, some AIX guys can lift 3 tires at IDENTICAL times because the subframes run all the way from the rear
suspension pickup point (
LCA front bolt) to the K member in front, are crossed perpendicularly in multiple places, and tie into the cage for additional bracing and support.
Since you're paying someone to do this for you, I'd say you're wasting your time/money. I've seen little to no differences between the brands other than some bad fitment on some of the really cheap ones and the higher quality ones involve tying the seat mounts in which is a nice feature. About the only thing they are going to help is with your door clunk, provided they are done correctly and your car isn't bent beyond repair already. Take a look at the OEM sheetmetal where the standard would attach (front) and where a FL would attach and reconsider this decision.
