I wouldn't say that it broke my Hopper 1. It is definitely much slower. But, if I had the option to have kept the Legacy UI, I would have not switched to CUI. But, the more you use it, the "faster" it becomes, meaning that it has less glitches.
Same experience here. I upgraded to CUI back in the autumn, when it first became available for Hopper 1. At first it was buggy and slow, now it's a lot better. Still a little lag in the DVR menu, but overall it's fine.