I have no opinion about Glenn, and have never rented a cat in the St. Pete area, but there are other two places in Clearwater that I know of. One is Clearwater Community Sailing:

http://www.clearwatercommunitysailing.org/rentals.html

They rent Hobie Waves for $25.00 / hr. You also have to pay $10.00/day per person for a "day membership".

The Sheraton Sand Key Resort rents some kind of Hobies. Phone (727) 595-1611. No idea how much they charge.

Jonathan