I must be in an alternate universe. The last month or two I've found wifi to be very available (10 out of 10 on my last airbus flights). I've been impressed with speed too, I think it's often as fast or faster than when teathered to my iPhone on AT&T LTE.
I know UA had a rough period last year and early this with roll out but I think it's fairly solid now (assuming you're on a plane with it installed). The only thing ice noticed is that it takes 5-10 minutes to fire up after clearing 10k feet (red to green icon) but after that it's been good for me. Well worth the $7-10 and far superior to the old flip down screens.
Clearly I seem to be in the minority.
BTW, I haven't tried using any of the free offers so I cannot comment on the speed there.