MP Megatron, would have to be my most less favourite figure... Those thin legs and how hard it was to stand him. I transformed it once and decided to never to it again... He is now in a box waiting to be sold!
I never got as far as attempting transformation as I was certain something would break. I did try displaying it but got fed up of it falling over and it's now in the same position as yours.
I think MP Megatron should have been non transforming so that a more sturdy, cartoon accurate robot mode was possible and included a detailed, die cast metal version of his gun mode as one of the accessories.
Takara would've have gotten some flak for the lack of an actual transformation but it would likely have been far more impressive looking than the mess they eventually released and wouldn't have had any issues arise over the alt mode resembling a real firearm.
Spanbauer,
In the case of Masterpiece Prime I think he was initially intended as a one off, then by the time Takara decided to go ahead with other characters they'd used their experience with Prime to help develop better techniques for making TF's in that scale and I think if G1 Prime got a new Masterpiece mold today the truck mode would look a lot more realistic.