I have ridden the FM E-Series, the 404 Revo and Reflex for a couple of seasons on trick and slalom.
The E-Series I gave up on after I had 2 extra cuffs sent due to pre-release. Of the 3 cuffs, 2 were manufactured wrong (they machine the cuff manually), and the original released too easily - and despite this, I never got a working replacement or refund. In fact I never got a reply to my last emails and voicemails. I ended up heavily modifying the boot to make it work. Note the e-Series failed on me in practice for a big event and took me bolting to the ski to get through the tournament.
The Revo is a heavy boot and could really feel the weight on the ski. The buckles for me degraded very badly and were non-functional after a season (admittedly I do ski a bit in Salt). I have also seen 2 failed 404 units, again at the weld area as mentioned by others. One resulted in a big yard sale at the wakes, the other went on the dock of all places!
I finally switched to a Reflex system 18 months ago and all is going well. I also picked up one of the slalom boots when they came out too. Yes the boot is a little softer for lateral support, but the quality is noticeably better, the release seems better built and the buckles are all good and still working fine with no obvious signs of degradation. I had meant to get the aluminum buckles, but they didnt have any when I ordered and these have been good.
Re the liner being thinner - I prefer the thicker silver liner and this feels almost the same as the FM liners which are admittedly more comfortable than the thinner black Reflex liner.
So on choice... Reflex all the way for me and I am happy with my choice. Safer, better quality and better support.
Disclosure: I am now a Reflex dealer (skier first), but only after I tried the bindings and would happily stand up for the product.