Rodales tests always give full foot fins better marks than the same model fin in open heel. Seeing as I dive open heel fins in cold water mostly, I've no experience with them.
I have a pair of Cressi SpaceFrog fins, which recently cracked - the LDS I was getting fills from that particular day said that it's not unusual, and that their Cressi rental fins last about 12 months before cracking or splitting - the plastic becomes brittle. The fins are great in the water though, and for $35, you can't complain! Mine were $280 AUD in Australia a few years ago, so I had good reason to complain.