I was lucky enough to find a Power Engine first series with FRFR speaker (although, in fact, reading the web I found that it was produced by Eminence). The convenience, compared to the next model with the Celestion Seventy/80, consists in being able to use the cab simulations. The final sound I like. I made a comparison with a Red Sound cabinet of my friend, and frankly, I have not found huge differences ...
The only problem is the absence of tweet that does not allow to use the Power Engine to prepare for the sounds to be used, for example, in a PA. If I decide to play only with PE, prepare the patches to be allocated for that purpose. If I only use it as a monitor, I prepare the plant sounds and equalizer of PE I make any corrections.
I also tested the model with Celestion speaker: to be used by disabling the cab simulations. On the clean sounds he convinced me, on distorted not.