I have had it on my Canon t3i for the last 3 years and love it...but I know just because it works well on one model of Canon...it may not be perfect for others.
We've been using ML on our 5D IIs for a couple of years now and have had no problems other than an occasional lock up. If it does lock up... turn it off and pop the battery... that should fix the problem.
ML is such an invaluable tool when shooting video on the Canon cameras that I hate having to use a camera without it. The exposure and focus assists are huge and the fact that you can see audio meters while shooting (what a concept). The only pain is that you have to have the magic lantern files on all your cards and if you make setting changes... you have to save those changes to each card individually.