The configuration of the API Audio 527 definitely has a lot more going on than most API modules and compressors in general, but for me this is definitely a good thing. I love having as much control as possible over my sound available to me, and this is definitely fulfilled with the 527. It's got traditional compressor parameters for output level, threshold, ratio, and a attack/release knob. It then has switches for choosing the type of metering you'd like (it's between gain reduction and output level), as well as for choosing the 'type' which is between new or old and for a unique feature called 'thrust,' which is unique to API compressors. I haven't seen a manual for the API Audio 527, so I can't say how well put together it might be.
The API Audio 527 really has an impeccable sound, and since there is so much control over this sound, you're also getting a very versatile unit in the 527. I've only had the chance to use it on snare drum and bass drum so far in my time using it, as I'm eager to try it on some other applications as well when I'm able to. I don't have one of these at home and have only used it in a professional recording setting, so I didn't have too much time to play around with it. I do however, think that it's sound will translate well for most applications because of this versatility.
If you're putting together a 500 series rack, I'd encourage you to check out all of the modules that API has to offer, including of course the API Audio 527. API makes some of the best outboard gear available and I trust their products to not only sound great, but to last and work day in and day out. I can't say enough about how well engineered the 527 is, and I really think that it is a module that most engineers will love using. Definitely don't pass over the API 527 when looking at 500 series compressors.