I'm not gonna comment much on the (ongoing?) "friendly" debate that seems to have started up, as I honestly don't want to be a part of it, but something near the beginning kind of jumped out at me...
They don't fit in with the grimdark setting of Spearbreakers at all.
Honestly, I think that if you're specifically trying to go for a specific sort of setting you are doing it wrong (I consider sci-fi vs. fantasy to be more a question of how the cosmology works than anything else). I actually really really really hate grimdark; it's been infuriating me for a while that the setting's been drifting in that direction, but I've held my tongue because... I don't really know because. I guess I was sick of fighting with everyone over every little thing. Buuut, since you've gone and dropped the big G-word, I figure now's the time for me to explain what I hate about this sort of setting and why, if anything, we should be trying to steer away from it.
I hate grimdark because, to put it bluntly, the entire genre is a one-trick pony. Nothing about these sorts of settings really ever fascinates me, because it's all just a monotonous, silly blob of CRAZYBLOODYGRIMBADASS with no actual rhyme or reason to it or anything special to catch my eye. In the mad rush to make everything as over-the-top as possible, the heart of the story is lost. I actually really liked the idea of the tin soldiers
specifically because they felt a bit out-of-place -- yes, they were a bit
too sparkly and magical, and their inner workings could stand to have been better-explained, but they (especially considering their backstory, which I find actively-charming) would be a really cute and whimsical addition to a setting that honestly really needs at least a dash of cuteness and whimsy to taste by this point. Even the ridiculously-sweet and saccharine MLP has things that break that mold (see: parasitic shapeshifters that mesmerise and drain life force from unsuspecting hosts) and I really think Spearbreakers, as a setting, could stand to get a little variety at this point.
I honestly rolled my eyes at the snack cakes, because they seemed ridiculously-random to suggest so specifically, but now, somewhat out of spite, I've decided that they really do in fact need to be included. With that exact name.
E: Also I think we should officially crown Aseaheru as the Thread Meatpieologist, because that was hilarious.