Sound — 9
I'm using an '07 Fender MIM strat through a Crate V18. I don't use any amp gain, it's always clean and if I want any gain I use the pedal. This pedal is classified as an Overdrive pedal, but it could be considered a fuzz pedal too. I mostly play funk, blues, and rock, but occasionally mess around with heavier stuff. In single mode, it sounds a little muddy when the knob is turned up higher at first, but when you start playing with the volume on the guitar, you can achieve a great slightly overdriven sound. If the pedal's knob is about halfway, 12 O'clock, the pedal will give a little break up, but works more as a boost pedal. In Double Muff mode, I typically keep the volume knob at 9 O'clock and the fuzz knob around 3 O'clock. On the neck pup, I can get a great Hendrix like tone here, and if I turn the volume on the guitar down it cleans up nicely for a SRV esque tone. With the guitar volume all the way up, the bridge delivers a tight distortion that is good for classic rock. When the guitar volume is lowered and on the bridge pup, I can get a crisp tone. I typically use that sound for blues rhythm, or RHCP type funk from the Blood Sugar Sex Magic era. It's great for playing bluesier stuff, especially on my strat. I also use this pedal with a Dunlop original Cry Baby. The order of my setup is guitar, Double Muff, Cry Baby, amp. The distortion before the wah has a really odd effect. The wah seems to control the amount of distortion when I engage it. If the wah pedal is all the way down, it has the typical effect of a wah, and the distortion is all there. But when you toe back, of course your treble rolls off, but so does the distortion a little. I personally love the two pedals effects on each other, but others might not. If the muff is after the wah, it is a little difficult to notice the wah at all. It might as well not be on at all, which is why I always put the muff first. I occasionally use this pedal with my Epiphone G-400 and it has a creamy sound through this pedal. My only complaint is that the highs are a little too flat for my liking, but that could just be the fact that it's a cheaper guitar. It can be a great pedal, you just have to play around a little and find a few of the settings that fit your style.
Overall Impression — 8
It can be a great pedal, you just have to play around a little and find a few of the settings that fit your style. The better features about the Double Muff are that it is really simple to use, and with a few adjustments, it can cover a pretty wide range of music styles, just not really heavier stuff. I wouldn't recommend it for anything heavier than Harder Rock like Led or AC/DC, but it does cover those two particularly well. If it were stolen, I'd be pissed.
Reliability & Durability — 7
I've had the pedal for about a year now and it still works fine. I've been using the same 9 Volt battery for the last 9 months or so and it still sounds fine. I don't know how it's lasted this long, but I'm not about to complain. The casing is pretty sturdy because it is made out of metal. The Only complaint I got on this pedal is that the input and output jacks are always going loose. It's really annoying because if you touch the pedal when you're playing, it makes the sound when you touch the end of the cable when it's unplugged. I have gigged with this before and I've never had a fear of it not working.
Ease of Use — 9
The Double Muff has a pretty simple setup. I didn't read the manual, you really don't need it because the pedal is really simple. There's a switch that determines if you are in single or double mode. Single being a slight overdrive and double being a semi heavy fuzz. In single mode, the bottom knob controls the volume and Overdrive level. In double mode, the bottom knob controls the output of the pedal and the top knob controls the amount of fuzz.