I'm now on my 5th flex disc in just under 6 years. The Meyle brand lasted almost 1 year. That's an improvement from the last candidate. Again I'm switching brands, finding one that is slightly more expensive this time.
I'm beginning to believe the issue is the high starting torque of the DC motor. I don't use 1st gear because it is very jumpy. I start out in 2nd gear and usually nail it.
I can tell the unit goes under a lot of force. The grade 5 bolts in the pic below were new 1 year ago. Notice how a shoulder has been worn on the ones at the bottom. I lost the 8th bolt on a turn, that's how I knew it was time to swap a new one in.