Well, they aren't the worst products, they are decent. The sub in question is cheap, so it isn't overpriced for its quality.
The problem with it is more that it is a 4 ohm voice coil, and running 300 watts into 4 ohms is going to cost you quite a bit of money. Do they have a 2 ohm voice coil version?
Sony is better than all of the following brands... 1) 2) 3) 4) 5)pyle 6)legacy 7)boss 8) 9) 10)road gear 11) 12)funky pup 13) 14) Seriously, though, I would recommend that you look into Kicker Comps or Comp VRs, maybe Adire Audio Shivas, Cerwin Vega V-Maxes, there are many better subs out there.
if you haven't bought them yet let me assure you listen to these guys. I wish I had found this site before I bought mine. Sq and SPL just isn't there. They sound like dodo and don't really get that loud. I agree with Jonathan, I'm getting ready to replace the sony's with the Adire shivas. Not sure how much a quid is but $125 is a great price for those subs but then I might go the rockford fosgates.
also i am in the same boat as KOZ. got some Sony subs before i knew what i was doing. now im upgrading probably to 1 Shiva in a 1.6cu ft sealed box with a Kicker 350.2. This setup is mostly a SQ setup. Hope it works awsome.