The front panel is laid out very simply considering the amount of options present. You can use this as simply as just being a preamp - basically just using the preamp gain for signal level and also the desired color of the tone, and then the output gain to get the level right. However the other elements are quite easy to use. The controls are laid out in a standard way as far as the parameters for the compression and EQ. One thing that may have a bit of a learning curve is that the compressor attack/release times are not labled in milliseconds - but rather a pot that has fast on one side and slow on the other. So you may want to play with that a bit to get a feel for the times. Avalon provides a very extensive manual, even providing you with some suggested settings to start with on certain instruments.
This is definitely a preamp that will color your sound - but almost always in a very good way. In addition, the amount of color that is added is something I have found to be variable depending on how hard you have cranked the preamp gain knob, and if you have the compressor working. The compressor has this crunchy, crispy sound that I love. I put a U87 through this preamp for vocals, compress lightly on the way to my DAW, and it sounds fantastic. It is a tube preamp, so if you have the gain set high, there is going to be a saturated tone. If you are looking for something more crystal clear - you may want to go for something like the AD2022 by Avalon.
I have been using this for about a year. I absolutely love what it does to the sources I put through it. Everything you put through this pre seems to become larger, and more up-front. So that being the case, it is usually best suited for things that are going to be prominent in your mix - perhaps vocals, a lead guitar, or a bass guitar depending on the song. This unit also can record a DI instrument, and I've had great results recording DI bass with the 737. This really is a great pre, and combined with a Neumann U87 mic it's hard to beat for vocals - you've heard this combo on countless hit songs, and actually it is very frequently used for voice overs in film and television. The compression sounds great and has a nice character, and the EQ is very smooth. Especially the highs. You can boost the high shelf at 32k, which sounds silly because you can't hear that high, but it DOES make a difference - it somehow affects the highest part of the spectrum that you can hear in a very attractive way if you need something to be a bit more airy and bright. One thing that I sometimes have a problem with is noise. With 24-bit recording it's tempting to get a very high level, and one shortcoming this pre has is that at the upper limits of the gain it provides, it begins to get very dirty sounding - which sometimes is good and sometimes not. The High Gain switch provided I have found usually introduces too much noise to be useful, unless you want it as an effect. This item is pricey, but I have found it to be a worthy investment. I'd buy it again.