Last week I borrowed a multy effect pedal from a friend. It was the Boss GT-001 (https://www.sweetwater.com/store/detail/GT001). I tested this with my electric guitar (Aria Pro 2, 1984) and with the Etherwave Theremin. I use a behringer K450KX amplifier.
The sound of the Boss is good but it was a little different from the sound when I plugged my guitar or EW direct into the amp. Is seems as if the sound is coming from a distance as if the speaker was at the end of a tunnel. It was a tiny difference but I did not like that.
I took me a while to get used to the pedal. It is not as easy as an single stompbox. But after a while I got the hang of it. I tried many patches before I decide to start with a empty patch and added effects to it. I tried the following effects: plate reverb, spring reverb, tape delay, chorus, octaver, harmonizer. Except for the spring reverb the effects are very good and usable. I did not like the artificial ‘drip’-effect in the spring reverb.The effects are good tuneable because of the parameters. Creating patches can also be done with the Tone Studio software in windows. This was a little bit easier then on the Boss itself.
I connected the Boss GT-001 to my linux pc and experienced that is was directly recognised. But when I wanted to use the Boss as an audio interface I was able to select it in Jackctl but I did not get any sound, only errors. With google I discovered that it must be possible to get it to work (adding a few lines to a driver and rebuild the driver) but I did not try this.
The reason why I was interested in the Boss GT-001 is that it has a build-in guitar to midi converter. On my linux pc I connected the Boss to Qsynth, choose the violin as instrument and it worked. I could play single notes on my guitar and they sounded as violin tones. I had to play very careful, properly and decent though, otherwise the converter could not do the conversion properly. Then I connected the Etherwave to the boss and tried again. This did not work at all. There was no sound except for some single notes that seems to occur randomly every once in a while. There was no response to movements of my left hand or right hand. So this is a nice gimmick for the guitar but not usable at all for the theremin. And this is a pity.
Conclusion:
sound: not as good as direct sound
effects: very good
audio-interface: does not work out of the box in linux
guitar2midi: does work out of the box in linux, nice guitar gimmick but not for the theremin