Having quickly played with this (as I look at options to avoid shelling out 279 Euros for C1 for something I don't use much) there are two problems as I see.
1) HDR Efex 2 doesn't seem to work. It didn't in Aperture either. Somehow it seems to screw up where it has to save the image to such that in Aperture the Google fix was to disable automatic re-import, save the image to the desktop and drag it back in. Ground round-trip experience - NOT. Seems to the the same with Photos. Using the other plug ins saves the image OK. HDR Efex, no idea what it does with them or where the saves go. Maybe I need to uninstall it and try it again with Photos. Not looking good though.
2) With Aperture, it would save a version of the photo so you would have your original and the edited ones side by side. Not here, it edits the original giving you the option to revert. Only way, from my admittedly quick look, to replicate Aperture seems to be to create a duplicate first. Then edit that.