@proofy
its hard to give a solid recommendation without them being on the market long enough to get some professional reviews, testing and consumer reviews flowing to base information off of.
the momentum on-ears tend to be a bit overblown on the bass with a v-shaped sound profile. this makes them good for bassheads but perhaps not for people looking for something else in a headphone. if they are designed to be similar to the on-ears in sound profile then you may want to think about if this suits your listening style.
i would generally suggest on-ear or over-ear headphones for gaming instead of in-ear. they will be more comfortable in the long run and for just a bit more than the momentum iems will retail for you can start getting into some decent quality full sized headphones. your choice though.
can you game with in ears? sure, if that is your preference. personally though it wouldnt be my first recommendation. in ears are better for travel, listening when doing activities and other such purposes.