I'm a little underwhelmed with this version of Grimlock. Why can we not get a good modern remake of this character? Classics? ...good alt, poor robot. Animated? ...not bad, but missing a dinosaur chest. FOC? ...good robot, but missing half the T-Rex.
In order to have the light gimmick work in bot mode, the dinosaur is missing its underside. Its just completely not there. It looks terrible from most angles; all hollow and thin. Probably acceptable as a deluxe, but not as a voyager.
Some fold out panels could have been included in rear of the robot chest cavity, to fill out the Dino underside. Would've prevented some bot lighting & maybe meant the Dino head would have protruded a little further out from the robot back, hey, that would've just made it more G1-ish.
T-Rex arms pop off quite easily too.
Robot mode is the stronger of the two, and what I will be displaying him in (which is a shame for a Grimlock figure - the dinosaur is/should be the main mode). Looks beefy and well represents the character. Nice articulation as well. Can get some nice poses with his two cool accessories (awesome sword!). I'm not loving the head sculpt tho.
This is my first non-Combaticon FOC figure, and I must admit the plastic does not feel great either. Still has that cheap feel like the Bruticus bots.
I would recommend him only if you really love the character (I do!) or the FOC toys/game. Or are a completist. Or really love transformers... 
For me, this should have been a deluxe with no gimmick. Would fit better with other figures too. (Unless grimmy really is that much bigger than OP in the game; I dunno, I've not played it).
TF Figs of 2024:
1) Legacy Magmatron
2) Legacy Gears
3) SS102 RotB Optimus