You can probably make up your own sump thats alot larger for less money expecially if your on a tight budget. The hang on overflow will not cause your tank to flood if its setup properly and kept maintaned. I clean my U tubes once a month and Every day I do a quick visual check to make sure nothings blocking the overflow intakes. When filling the sump you need to know where your max water line will be after accounting for some back wash from the tank via the returns. keep your operational water level below the point that holds it and the back flow and yoru fine with power outages.
I would also leave the powerheads in the tank for extra current. Its nearly impossible to have to much flow.
A home made sump can be made out of a 20 or 29 or 30 gal
tank and some plexiglass and silicon to make some chambers. Add the overflow, plumbing and a return pump. Regretfully the return pump and the overflow is going to come close to your budget. The overflow you have pictured will require additional plumbing as well as a return pump to get the water back to the tank. I also dont see where the return is to connect on the sump as the top fitting is for the drain line from the overflow.