The thumb sticks aren't great on this device to be honest but they aren't the worst I have encountered either. I have squeezed over three years out of my 7800 and the left thumb stick has only just gotten unusable - not bad for a cheap(ish) Chinese handheld. I'm going to attempt to swap out the stick (bought four direct from JXD) and will post my progress with pics when I get round to it.
I have been happy with the 7800 generally, if you get round the sketchy build quality and get a decent custom rom on there, I have found it a great device for all of the older emulation which was my main reason for buying it. Screen ain't half bad either.