I held off buying one of these for ages because I saw no advantage in having a controller which rumbled an could potentially break your concentration. However when one of my SIXAXIS controllers started suffering from over-COD-ification (constantly running in Call of Duty kills the right stick) I plumped for a DUALSHOCK3 and haven't regretted it.
It's more than simply rumbling, many games use the vibration alongside visual queues... if it wasn't for that little buzz my horse would have bucked me far more in Red Dead Redemption and it helps in racing games to know if you're clipping curbs!
Those who're adverse to the 35 quid price tag forget that it plugs into the existing controller charging cables (which incidentally are as cheap as chips USB cables) and doesn't require extra outlay to go wireless, not like the Xbox controllers. I also like the fact the lights are front-mounted, meaning that when it's almost time to charge you're not distracted by constant blinking like on the Xbox. There may be some third-party wireless controllers for cheaper, but these ones beat the rest hands-down for sturdiness and reliability.
All-in-all I'd say to get one of these as soon as your SIXAXIS starts to wear a little, you won't regret it.