I considered joining Jamplay, but in the end I went with guitartricks instead.
The deciding factor was that it seems to me that jamplay employs high profile players as teachers and use their names to attract subscribers, which can be a good thing, of course.
But to me this strategy works the other way around. I’d much rather learn from a dedicated underdog with good teaching skills than a super guitarist lacking teaching skills.
Just my personal opinion <shrugs>, and I might add that a year in, I am more than happy with guitatricks.