I have the Inon UFL-165AD (fisheye) myself and it really changed the way I took pictures UW. If you like wide angle photography and you don't want to splash out on a full SLR set up this is a really good option. It isn't exactly cheap and only really good for underwater but it is a fraction of the cost of the other alternatives, not to mention that its is fairly compact for travel.
It gives you so much more light to play with and for my Canon ixus 800 it gave me really nice results, a huge improvement on what the camera could do before.
This has to be my favourite picture I have taken using the lens:
http://www.pbase.com/ozanners/image/83991135/large
Here are some others:
http://web.mac.com/ozanners/Anners/Photographs.html#27
http://web.mac.com/ozanners/Anners/Photographs.html#25
One thing I would say is that it can be prone to flare, from what I read most fisheyes are vulnerable to some degree, and blacking out the silver parts of your cameras lens should help minimise it.
I also bought a couple of Inon UCL-165AD (close up) at the same time along and I hardly use them because I enjoyed the fisheye so much, but saying that they give great results too. You can even stack them to give even closer macro:
http://web.mac.com/ozanners/Anners/Photographs.html#32
Make sure Inon make the adapter for your particular housing first though.