Colarndo, a longer release time does not give you more sustain. Generally, longer release time is used for transparency reasons. In fact, if you think about it logically, a longer release setting may actually kill your sustain!
To get more sustain, you need to compress more and turn up your make-up gain. That might colour your tone, though. So it's a tradeoff.
Also, a good compressor may not necessarily be a subtle one. It really depends on what you want and how you set it.
And anyway, I recommend that first-time users get a compressor with more knobs (more adjustable settings), so that you can play around and discover how it affects your dynamics and sound.
Hope I helped!