On an errand at a local Target, I stumbled on a goldmine. I found a small Sherman III tank toy, on clearance after Christmas. I snatched it up at about $1.50 and took it home to compare with my Fireflies. Sure enough, my modeller's instincts were correct, and it was at the very worst extremely close to a perfect 15mm model!
Some details left me wanting: the gun was way too thick, the plastic-rubber of the tracks, while well detailed, was solid, and some of the hull details were simplified for a one-directional injection mold. There is no doubt the details are less accurate than on most available kits. However, to bulk out a force of nearly all Sherman tanks, why not do it for $12?