Been running a lifereef overflow on my 55 gal for a few years now and never had any issues despite numerous power outages.. it has never lost its syphon! I highly recommend them!
I bought my first tank used, and it was setup with the U overflows. I hated the one that I had. It would loose siphon all the time, and it flooded my floor more than once. I put up with that setup for nearly a year before I just bought a new drilled tank.