Hello,
I am new to the forums too, and am scanning for threads relating to the SP550-UZ (which is what I own), hence finding this thread.
I purchased my SP550-UZ about 3 months ago, and have since been on 2x dive trips using the PT-037 underwater case with diffuser (no other accessories as yet, this is why I joined the forum to find info on strobes/rigs etc).
I am only an amateur photographer, but in my view the SP550-UZ serves me fine. I read some reviews with cons on certain features (focus on zoom at 18x in low light for example) but in reality streatching the camera this far isn’t why I bought it.
Anyway, I have no problems with it and it provides superb quality shots above and below water. Macro and zoom are great, as is the wide angle.