I just want to say some points, because i saw some comments in the twitch chat.
Yes you get very fast vet3 with this units, BUT the vet does not really care for the flamerhft.
You don't get really strong upgrades for it.
It is always a back and forward: flamerhft is on the field, allies are in trouble. T70 is on the fiel, axis are in trouble.
Hmm I am 90% sure that vet 3 gives a bonus to the flamer cooldown, IIRC it was part of the Halftrack rework. (Upgrade on 251/M5 means you can no longer reinforce; all HTs have shared veterancy if they dont have an upgrade)