No undercarrage to take any energy away.
Well it's not as if they really take the energy if you ditch conventionally either...
There have been several instances where CAPS have been deployed over water with successful outcomes; the only which wasn't was at very low altitude.
For a fixed gear aircraft if I had a chute I would pull it every time if I had to ditch, I know from having flown seaplanes just how likely the gear is likely to flip you over and I'd much rather maybe have a back injury and pretty much guarantee landing the right way up than run the risk of being upside down.