I've had these for just under a year, mostly used the middle sized one (figure of 8), but not excessively, perhaps a couple of sets of 30 bicep curls a few times a week. The band has snapped near the join. Luckily I noticed it was going, so it didn't snap when under strain.
I've moved onto the smaller band now but I expect this will also 'go' in time.
They are only made from some sort of vinyl/rubber material so they are bound to perish in time, but I did expect they would last longer.