Lets compare again (anyone pls correct me if im wrong, or add to this list):
1. Megahouse version is slightly bigger.
2. CM's has 'some' die cast parts (probably the silver parts near the engine), while Megahouse don't seem to have any.
3. In spite of above, CM's ver looks more plasticky overall, perhaps due to color and less detail. Megahouse ver color and detail is better, IMO looks better overall.
4. CM's figure-to-bike proportion looks ok. Megahouse's bike looks too small for the figure.
5. CM's not yet seen any pictures of characters' faces, maybe can't even remove helmet or can't raise visor. Megahouse we have seen the characters with helmet visor raised, and also w/o the helmets.
6. CM's seem to be fully transformable. Megahouse may need to remove/swap parts. Not confirmed.
7. Megahouse Rey comes with bike storage boxes (and little accessory stuffs like drink bottles etc not sure if included?). So far Stick's don't show any storage boxes with his set. CM's both sets come with bike storage boxes.
8. CM's pictures show wrong character matched to the bikes.
should be:
Stick is supposed to wear red body suit, knee armor shows a bit of blue - matched to bike with name S.Bernard, shoulder number 21.
Rey (or Ley) is supposed to wear blue, knee armor shows red - matched to bike with name Ley, shoulder no number (according to anime) or at most a 31 (old Aoshima/ Imai model kit)
Well, maybe we can just swap the figure to match the correct bike (i.e. #21 match red body) but then if the face is visible, then we might have to swap the heads.
Unless CM realized their mistake and corrected it before release.

PS > Seems like Megahouse has some sort of mail-in exclusive to give away extra weapons set but there's little hope we can get it... (although i really want it bad

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Link here (scroll down)