Since the latest patch, Pgrens are considerably more fragile, and require the same cover micro as any other unit in the game. As with conscripts, grens, and penals, cover is supreme. Think of Pgrens like Penal troops with a potential for AT. With good support and shielding from Grens and a Halftrack, a Schrecked up Pgren squad can stay on the field longer than a tank.
As stated before, the need for Pgrens is situational. If the enemy has invested heavily in AT guns, Pgrens will be much more survivable than a tank. If the Soviets have a lot of tanks, then you may be better off spending your MP on AT guns. HOWEVER, Pgrens eat SU76s, SU85s, and Katyushas for breakfast. One flank can totally ruin the day of any turretless tank destroyer or light vehicle.