I do not use LUTs, I find I can grade easier and get what I want, not what someone else thinks I want.
I have used Cinema Grade a lot, it is useful in specific situations. In most situations it wastes too much time not achieving what I need. Especially with the latest FCPX update, it seems to be wonky. Waiting for an update to fix it.
I find the built-in color grading tools to work wonderfully for me in 90% of my grading and correction needs. Others will have different experiences and approaches. You're asking a very subjective question, so grain of salt with each answer.
I agree with FCPX.guru. Do most of my own colorgrading for the same reason.
Also helps me to get better if I have to do it. It is more time consuming but I like it.
I can imagine some situations where you need a LUT that has allready done.
My grain of salt.
I own both of those plugins and happy to offer my opinion. I also own a number of LUT packages that you can use with these plugins. However, as FCPX.guru and others have mentioned, the FCPX built in tools are excellent and powerful and if I need something more or specific I’ll usually export an XML and grade my project in DaVinci Resolve.
All that said, between the two - mFilmLook and CinemaGrade - I prefer mFilmLook. You can produce good results using either plugin but, imho, I think the mFilmLook UI and the access to more adjustments in the traditional FCPX Inspector panel is a more elegant and robust integration than the interface that CinemaGrade provides. mFilmLook also has a few more bells and whistles like adding flares, distortions, etc. CinemaGrade has grouping and shot to shot matching. If you just want to apply a LUT to your footage either program will do that too - actually don’t need either plugin to do that as FCPX offers that function built-in.
I’ve read reviews that say that CinemGrade is aimed at folks just learning about color grading. I suppose mFilmLook would fit in that category too. Both are relatively quick and easy to use. Again, as others mention, I suggest learning about and getting the hang of FCPX’s built-in color tools - they are pretty powerful. Or download the free version of DaVinci Resolve and experiment with its expansive color tool box. There are a number of tutorials you can find online on grading, color correction or creating “Looks.” There are lots of free ones on YouTube or get cheaply from the always excellent Ripple Training website. You may be pleasantly surprised with what you can produce in a very short time.