My MP1 can stand, although admittedly it is more prone to tipping over than other MPs.

MP1 has metal on the chest and legs, whereas toys like MP Megatron, Rodimus and MP22 Ultra Magnus have metal feet but the rest is plastic, allowing the metal feet to act as stabilising ballast. MP Megatron needs the metal feet to counterbalance the weight of the massive fusion cannon. It's unfortunate that the feet are prone to rust, but I haven't encountered this issue w/ MP Rodimus or Magnus, so it seems that TakTOM learnt their mistake from MP5. This big toys are more prone to falling over during play, and having weighted feet really helps to stabilise them. So in this sense, the use of die-cast metal is used more for practical reasons rather than cosmetic one. Although I don't mind metal being used for cosmetic reasons, so long as it's done properly. I don't mind plastic toys... I just wish that some of them were cheaper. e.g. Alternities cost about as much as Binaltechs, despite being smaller and more plastic!