The back cover of MF0:Firebrands features a trio of mobile frames, but the late-model Osprey conceals a lot of the other two. Anyways, the individual illustrations:
Late-model Osprey

Just wanted to mention that the square patch on its left thigh is a QR code giving basic info about the unit. The small hatches on the shoulder-shields are flare & chaff dispensers.
Conscript/Commissar

Lots of jury-rigging on this one, including the entire right arm. There's a cutting torch bolted on near the pivot of the pincers. The handheld weapon is a simple, triple-tube rocket launcher with gravity feed.
Chub

To reflect its owner's aristocratic status, this has a good deal of custom-built applique armour which is both decorative & functional. The upsized anti-materiel rifle is intentionally designed to resemble a lance, referencing its long reach & anti-armor capability. It's also a bit of a dichotomy, in that its length makes it unwieldy for anything but combat at long range. The weapon's appearance, minus the shroud, was modeled on the EM-2 rifle. The military pick is for melee combat, and has a rocket thruster built into its head for additional oomph when striking.
I was considering a set of flip-up wheels behind the heels to resemble rowel spurs, but I totally forgot about it.