Penals were originally 360mp and they beat grenadiers in a long range fight, but Relic decided to reduce their cost and turn their SVT 40 rifles to more of a close/medium range weapon, they usually need VET 2 or 3 to be effective on the field, otherwise they just die, and if you build a T2 to get some AT, you are going to delay your teching very much and probably get pushed of the map if you get too many penals
(Their Veterancy increases their accuracy by total of 60%, so if there are some LMG´s laying around on the ground, pick them up with penals, and you have a squad that shoots down everything, like the original Obersoldaten, since a LMG 42 has good stats, but when you increase its accuracy by another 60% its going to be godlike)
I have been theorizing that one should combine Penals with the Brits doctrine that can call the truck that drops weapons to make Penals with too LMGs (or what that gun is) each.