I have an ESP EC-50 and this guitar absolutely crushes with this pickup in the bridge position. I may get the 24V battery kit to get even more response out of the pickup.
I have this active EMG 81 in both my LTD EC-401B and EC-401. While I find this pickup goes incredibly well in my baritone, and brings a nice amount of attack and compression to it, which compliments that guitar really well; I don't like it being in my other EC-401.
I use said 401 for my pop punk/hardcore band as well as playing other rock, metalcore stuff in between. And while this pickup works remarkably well when you're playing palm muted breakdowns and core riffs, it does NOT do me many favours when I'm writing playing my pop punk riffs and other stuff. The compression that comes with this pickup doesn't tickle my fancy and I don't like that I when I dial back the volume knob for a slightly cleaner tone, it just dials back my entire volume rather than dialling back to a cleaner output.
I also find it much to harsh for my crunch tones and not very dynamic when it comes to clean tones.
All in all, don't take this as a bad review on the product itself. The pickup is a really nice pickup and I like it LOTS in other situations.
I just don't believe it's for ME in the music I write with my band. It is a great pickup if you're playing metalcore with fast, attacky riffs and lots of huge breakdowns. And yes, lots of pop punk bands also use EMG 81's and sound amazing, but I find that for my particular sound, they're just not quite right. Still a great pickup!
I use the 81 in pair with the 85 and it is just the perfect set up for all your metal needs. You can get some blazing hot distortion and some crisp cleans as well. I plan on using them in future shred machines!