I enjoyed my Focusrite 56 very much, the liquid pre's really do have sonic differences that are noticeable on them.
For what price they're offering these at, it's worth it IMO.
I did however get to a point in mixing where using a unit like these was no longer sufficient, as their processors get "taxed" heavily when adding vst/au/rtas plugins on channels and it will start to perform slowly, causing you to really push back your latency.
The best thing that I found to do when using these is to track at lower volumes (less than -12db, more than -25db) to get a solid sound that's not distorted (in a bad way).
I would track EVERYTHING that you're going to be tracking to the mix BEFORE you start to add plugins, esp. on the 2 bus mix out of your DAW. If you don't do this, and begin "pre-mixing" (which I now realize isn't correct at all!) you'll have serious latency issues and the delay will be noticeable on the headphone mixes to the players recording and will cause problems.
Other than following simple steps that we should all follow in workflow, this unit is great for what it is!