I've had the Tunze Osmolator on my 115 gal tank for over two years and it has worked perfectly.
I used the Aquahub DIY kit from BRS with a Neptune PMUP on my 30 gal for almost as long and it has worked perfectly.
Both take a little maintenance, periodically cleaning the optical eye and float switches. If either get built up with film or growth it will cause a problem, and has been the only reason I've ever had any trouble with either one. In both cases it prevented the pump from running, which is probably better than a pump not shutting off.
Haven't had to replace the Tunze pump yet (uh-oh, I just cursed it).
So, in my experience quality equipment is certainly important, but proper maintenance just as much. Pretty much goes for all equipment.