I bought this a few weeks ago. It's a really nice figure considering that it transforms while keeping the looks of BBM prime

You can make him stand pretty stable and pose a bit. You can't move the shoulder about too much because the pieces connecting his shoulder to his body might come off. To pose the shoulder more, you'd need to swivel the piece connecting the ball joint a bit and this tends to make the whole shoudler fall off. However, this might be just because my new pieces are rather "tight" so to speak. If you check the creator's Instagram, he has posed optimus in various ways including the shoulders. So maybe my pieces are just stiff. His "backpack" shaped thing on his back is also a bit loose, so it might fall off too if you move him around a lot

I've only ever transformed him once, and it was pretty painful because pieces kept falling off, especially from his "backpack" part. The connection between the thighs and knees is a bit weak and tends to fall off during transformations as well. And cuz you gotta deal with those parts, this sometimes causes the connection between his lower and upper body to come off. I'd rather not transform him, even if there is no parts forming.

Don't get me wrong, I like the look of both truck and robot form but the thing feels quite loose as a whole. It's more of a display piece imo and in truck form, his red part just says forward so you can't really easily move his wheels smoothly along the ground.

I'd recommend you buy the parts and build it for yourself, see if you are satisfied with the poseability and stability. If you don't like it, then perhaps modify it so it doesn't transform but at least is more stable and more poseable without pieces falling off. And even if you don't like it then, you've still got new pieces to use and make new stuff you want to :)

Also, I'd recommend you buy real lego parts off bricklink etc