The Peltors work the same way as the Pro Ears as far as I can tell. I believe the MAG model has a NRR of 29. That's the highest rating of any of the electronic muffs that I've found. They are also the most expensive.
I've tried both (borrowed) the Tac 6 and Tac 7 muffs and really like them.
I just got a pair of the HP-1's over the weekend and if the weather allows, I plan on stopping at the range on the way home from work tonight to try them out.