I purchased it and am using it now. A lot of nice features, but one disappointment is that there are no scopes in the base correction and final grade modes. There are in shot matching mode (thankfully), but in order to establish correct levels for base correction, you have to make your adjustments by eye and then after sending the clip back to the FCPX viewer look at the FCPX scopes. Usually more adjustment is needed, so back to the Cinema Grade UI to adjust. This back and forth is unusable for me, but I'm hoping the addition of realtime scopes in all modes is a future update.
The workaround is to base correct in FCPX, and then use Cinema Grade for final grading.