For a simpler inexpensive envelope filter, try the tonefactor (or mojohand as its now called).
I had the Frostwave funk a duck and its an incredible filter, but expensive. Its built real well and needs a wallwart to operate.
I also had the Mooger fooger filter, but its also expensive,large and sucks alot of tone.
tried the emma and tonefactor - kept the tonefactor, more organic and richer sounding - I keep a nice comp after it (BJF) to restrain the beast somewhat.
LOVE it with reggae.
The EMMA, Maxon, and Guyatone FLIP FB-X Funky Box are good ones, so is the Tone Factor Analogue Filter 442, but to me the best I have played is the MXR Envelope Filter, it is very wet sounding.
ill tell you upfront that a lot of people have a problem with its size, but if real estate isnt an issue for you then id say this might eve be a better choice than a mutron. very similar jerry garcia type tone, and under 200 on ebay. also doubles as a phaser, although it isnt great
Not a bad idea if you're not sure. I've had the mini-Dano and the Ibanez soundtank autowah. Later ran across an old Ibanez AF-201 that costed many times more. The AF-201 is richer, more organic has more quack and many different sounds. Neither unit though could be called "transparent" or true-bypass. After all the effect is a filter, meant to screw up your tone and change your sound a lot. /C