They have a shorter life span on parts if you run them on the pulse mode constantly. It's cheaper to buy the pieces to fix them when they break then the new wet assemblies as a whole. The rusting out on the older models will be replaced for free if you send the pieces back. They will rust out, the impellers will seize, the inner plastic piece chips where the impeller goes through it pretty regularly and customer support is less then great. Other then that they move a ton of water and run relatively quiet and take up less space in your display
I've had more trouble with these pumps in the long run on the 18 tanks that I take care of then anything else (except maybe the Aquaillumination LEDS)
Oh yeah and if you get the battery backup make sure to get the new cable as the old ones were recalled for fire hazard.