Hi,
I actually used the FL20 with the PFL-01 housing. It attaches to the housing via a sync cable. There's a small cable that comes with the housing for the strobe that will attach your camera's hotshoe to the housing. I'll disagree, and agree with some of the things said above. First off, I've enjoyed the flash, the hardwired (fire every time) TTL, and was generally pleased by the amount of light given off by the strobe. It was a great beginner strobe as I didn't have to worry about correct exposure. The big bonus of using that particular strobe is I could completely turn off the internal strobe and therefore almost double battery life. Additionally, since it has its own batteries, your camera will cycle faster because its not charging the strobe. Finally it makes a nice topside strobe out of the housing. Those are the good points.
The bad - The strobe housing is square, awkward to aim correctly and the external diffuser is a waste of material (rarely stays attached correctly). It also doesn't have any place to mount a fiber optic cable should you wish to add a 2nd optical strobe down the road.
My recommendation - It will be better than most low end strobes and if you're not planning on going to DSLR, or adding a 2nd strobe then it might be a nice strobe for you. It will work fine for all of your fish portraits and macro shots.
If you're planning on doing quite a few WA shots, adding strobes or the possibility of upgrading a DSLR exists down the road, then invest in something a little more beefy. Looking back on the issue, I have no regrets because I was new to the game. If I were doing it today I would buy an Inon D2000 strobe.