Though, when you get a chance to use those thompsons they kick absolute ass. Seriously, most people are used to vehicle crews fighting as well as RETs more or less. With thompsons, they perform almost as well as sturmpios. I like to get them on my stuart crew. I find they can come in handy in a few ways:
If you can close with an under or unsupported AT gun you can mow it down in 2 seconds. I've even pulled this off under light AI fire, you can afford to lose one crew member. This can be a massive swing in a fight. Remember - cap or kill the AT gun. No freebies for the enemy to re-crew.
When I'm trying to escape a shrek squad sometimes I bail out if they only have 2-3 men. This causes the shrek to shoot at the crew not the tank, sometimes saving it. With thompsons, I occasionally wipe the squad. I also use true sight by backing around a corner, bailing, then charging back forward.
If you are good at preserving vehicle crew vet but not so much at preserving the vehicles themselves, you usually end up with a few spare vehicle crews. Thompsons make them effective close range support and they can assist with repairs.
Now, I think that 90 mun is expensive for what you get, but a cheaper price might mean seeing combo's like M10 spam filled with Thompsons. I can only imagine the horror of an M10 swarm crushing infantry and then the crews bail out and mow down the retreating infantry... Yea.. Ouch.
I see a few ways that the upgrade could be improved to make it worth the 90 munition cost, mix and match:
Instant Bail - The 3-4 seconds to bail in combat gets many crews killed before they can escape, making thompsons unappealing. Upgraded crews should bail just like out of combat, instantly or at least much faster.
Some Crew Survives Vehicle Kill - A guarentee that 1-2 crew members survive with low HP when the vehicle is killed.
Scuttle Vehicle Kit - Essentially the reverse of repair critical. Spend ~10 muns to cause heavy engine damage or imobilization, plus damage equal to about 1/4 a shermans HP, to an abandoned vehicle. The idea here is that people don't want to bail and hand the enemy a tank. This way they can quickly destroy a weak tank or at least cripple it to slow down an enemy recovery effort and counter attack.
Also..... Can the M20 crew please, please upgrade the three non-zooked crew to thompsons, M20 is the perfect vehicle for the thompson upgrade...