I used to be on this years ago, and I bled for 6 months ! They did tell me that I should have rung back when I realized and they would have given me the next one straight away and that should have stopped it. It did take till 6 months to stop the bleeding, even if light, I then had two more jabs before I came off it to try for another baby.
I did find I was a little more highly strung when on it, but am more prone to mood swings anyway I think, so worth keeping an eye out, but other than that a really good contraception, and great to have no periods for swimming etc
Do plan ahead if you want another baby, as it can take a few months to get your periods/cycle back to normal after having these jabs ready to try again