I've bought 'other brands' before for the likes of the N64 and PS2; most peripherals work fine - say rumble pack for the N64 or memory cards. However I learnt a valuable lesson, controllers must be original - always buy SONY. The buttons work perfectly, etc, and any complaint with function would be sorted Im sure.
The build quality of the Sony controller is great; people say its more rugged and durable than the original non-vibration version, Im might slightly agree to this. It certainly feels solid; but the weight difference is minimal - not heavy.
It may feel clunky and seem to have more battery life compared to my old original controller, but lets face it, its well worn and all batteries suffer memory-loss. Im expecting this one to last at least 2 or 3 years with hard frequent use (daily).
Is it worth ten pound more than the non-vibration sixaxis? Not if this is to be a spare controller; but yes if you're going to play often - it brings many games alive; driving games etc. I can vouch that it works well with Killzone 2. At 35 pound its good value IMO.
Be warned that this is the controller only - no USB cable. (cables are cheap and common).