The A-Designs EM-Red is a 500 series microphone preamp that is part of A-Design's line of mic preamps. There are a few others that are different colors both in sound and look. The B room at the studio where I work has a rack that's loaded up a bunch of the A-Designs stuff, including EM-Red and a few others in this series of colored preamps. EM-Red in particular just has a 1/4" input in the front - you get the rest of the connections from the Lunchbox 500 series casing. It's not usable or rackable outside of this 500 series rack...
Using the A-Designs EM-Red mic preamp isn't difficult at all. There isn't going to be anything out of the ordinary found here, as it's just got the essentials for you, which is something I certainly welcome as it's super easy to use. What you do have to work with are buttons for 48 volt phantom power, a -20 db pad, and a phase reverse button. Simply set your level coming in with the gain knob and you're all set to go!
The sound of the A-Designs EM-Red is definitely that of a professional mic pre. It's also got it's own sound and I'm not sure what kind of well known preamp I might compare it to. I have found however, that this is an awesome microphone preamp for recording guitars of all types. I've used it mostly for recording electric guitar, but also for a bit of acoustic and mandolin as well. It's a super clean sounding mic pre and when used with a great microphone you really get all of the detail you want in there.
The A-Designs EM-Red and this series of mic preamps in general is something everyone with a 500 series rack should be aware of. Unfortunately you can't really try each one in the series out before buying them unless you've got them on hand elsewhere, but each of them definitely has their own sound. The EM-Red is probably my favorite for recording things that require attention to detail. Ideally it's great to have a few different EM series preamps in your rack to get a few different flavors, but if you can only have one, the EM-Red is as good a choice as any...