If you go over to ReefCentral.com, and look at their forum, you will find a huge thread (over 300 posts) of Rio horror stories. Most of them involve either electrocution of tank inhabitants, shocking of owners, release of oil or copper into a tank and other horrible things.
I had a Rio pump running the Protien Skimmer in my reef for 4 years. One day, I came home to find all of the power in my tank off, including my lights and heaters. I found that the 20 AMP main breaker in the circuit breaker panel had tripped. When I reset it, it tripped again. So I started looking around. When I put my head near my sump, it smelled like an electrical fire. I pulled the Rio out (with the power off) and found that it had cracked and released enough current into the tank to trip my main breaker (thank heavens I had a grounding probe in the sump). I used a bunch of carbon to get the crap that the power head released out of the water.
I was lucky, I didn't lose any livestock or my life. Others have had much worse experiences.
Avoid Rio, unless you like to kill fish.
Don