Hello,
I have a sunsun HW-304A on my 27 gallon cube fish tank. It has been on there since last Christmas, so more than 10 months now.
I can tell you this:
1. DEAD SILENT. I have to put my ear up against it because I can't tell if it is on or not.
2. Absolutely tons of media room.. I haven't filled mine up all the way, but I bought a roll of media and I've got 3 trays full of those filter pads (3-4 per tray) and the remaining tray with the bag of (included) ceramic rings. I need to buy a tub of seachem matrix to fill it with.. But because it's working so beautifully I don't want to fix what isn't broken..
3. As I have the 'A' version, it does not have a UV bulb. Here are a few things I have heard about them:
-Only 9w, therefore it does little to no good with the flow rate of this filter.
-If used for a long period of time, will cause degradation of the filter media baskets, as they are not UV resistant plastic
4. Tubes.. I would replace the tubes they give you with OPAQUE (black / non-see though) ones, as the green ones they provide are nearly identical to the eheim ones, they let light throw and now there is a ton of algae growing inside them (I haven't bothered to clean them, but if I ever get a new tank and bought a new filter, I'd buy black tubes to replace)
Overall: It is great for the money, you will not regret it.
Hope this helps,
-1998golfer