I use mine all the time, albeit in a work environment but use them often enough at home to that i think they're worth the cost.
I definitely prefer the offset reversible type, often you'll need that offset to be able to turn the fastener against a flat surface and the switch gives you a safety barrier against backing yourself into a corner (seen it happen, guy had cut the bolt and replace).
If you can get a good set of zero-offsets cheap than perhaps just stick with them, i wouldn't bother with a flex set unless you need them, the movement of the head can be a pain when your trying to keep it on the fastener.
I like Facom but they're a bit pricey, whatever you get make sure to get a set with a warranty that covers the moving parts, i can pretty much guarantee that you'll strip one out eventually especially if you start using them often.