Sound — 7
I found the Pocket Metal Muff excessively bright, and needed to bring my amp's treble down to compensate. Its distortion is cold, edgy, and tight. This is not necessarily a bad thing; many "metal" style distortion boxes have way too much bass that only muddies up at loud volumes. In my opinion, the "Scoop" switch was best left off, but some players may like less midrange than me. Different settings of the knob and Switch did not drastically alter the Metal Muff's tone, but colored it in a somewhat subtle way. The pedal is designed to be flat-out all the time, and I found the tone to be heaviest with the Gain knob on 10. Bummer it doesn't go to eleven! I miss not having at least a bass and treble pot, which would increase the pedal's versatility. You can only have so many knobs and features on a pedal this small, though. If you're into metal or industrial, this could be the pedal for you.
Overall Impression — 8
This is not a sound I would use for my main Live tone, but I would consider getting one for studio use. Its cold, bright distortion would be great for filling in frequencies that might be missing from your recorded tone. Like its title implies, you won't find any blues, country, jazz or even classic rock tones here. If you're constantly looking for a heavier tone, give it a try. Especially considering its extremely reasonable price tag of $65 or so, the Nano Pocket Metal Muff is well worth having around.
Reliability & Durability — 8
The case is unfinished cast aluminum, so you're not going to break that no matter how hard you step on it. The construction seems solid and the soldering inside is very clean. The only reservation I have is that the jacks are mounted directly to the circuit board. Be careful that you don't step on the cables when they're connected, as the jacks' solder joints my break and ruin your gig. Besides that, you should not have any trouble with the pedal.
Ease of Use — 8
The Nano Pocket Metal Muff, Electro-Harmonix's latest product whose title could be mistaken for a sex toy, is incredibly easy to use. One knob is for output volume, and the other is for distortion. The mini switch in between is labeled "Scoop," and can be set to Hi, Lo, or Off. In lieu of any other tone-shaping controls, this Switch pulls midrange frequencies out of your tone; Lo for a moderate reduction, Hi for a more drastic cut. This is clearly a pedal aimed at the player Who doesn't want to deal with lots of programming, menus, and other non-user friendly things you might come across in a more complicated device. Its "nano" size is notable also; it measures a mere 4.5" by 2.5", which is great for those whose pedal board real estate is at a premium. I took one point off for the lack of a separate battery compartment. The bottom cover needs to come off to change the battery; this is minor but annoying.