PzIV and PzIV Command are identical, the higher fuel cost is due to their boosting ability.
Health and armor-wise they are identical. The P4 command tank is faster, but it's gun is significantly inferior to that of the standard P4 vs armor. It's mediocre against infantry, somewhat better than the normal P4, but not especially good (esp. compared to the Ostwind or KV8).
So you're paying more fuel and manpower for a 0.8 received damage modifier that only works on friendly territory and for much worse performance against vehicles than a normal P4 with a moderate anti-infantry buff.
I haven't had the chance to use it much, but it seemed fairly unimpressive the last time I did. It doesn't dismantle infantry like the original P4 IST did, and I didn't notice the defensive aura really swinging any battles moreso than an additional Ostwind would have.