If the counter is to run a way its a pretty fucking good ability...
The thing is, if you attack normally, the squad would run away anyways. Except when thompson paras pop the ability, you'll get basically a guaranteed squad wipe regardless of what the enemy squad does. Meanwhile, mp40 storms might get just an extra man killed compared to just normally attacking the squad. Essentially u pay 25 munis to kill an extra man, while thompson paras pay 20 for a squad wipe. I've done it so many times with the paras, it's almost unfair, I just get them on your retreat path, wait for the retreat and pop the ability on even a fairly healthy retreating squad, then squad wipe. It's pretty damn easy to get on a squad's retreat path.