For starters, EHX says it won’t track the low E string. I have played my bass with the Mel9 in my living room. I think the cello setting would be great for some stuff. The orchestra setting generates notes one octave above and below (at least) so two note chords on bass would be cool. Tracking was good. The Mel9 likes a good hot signal and bass should supply it. I get some bass gigs now and then & I will take my Mel9 with me to the next one. I think you will like it!
Andy

You’ll get better results keeping the dry signal louder than the wet signal which can hide some of the tracking artifacts. If you want to run effects after the Mel9, put it and everything after in an fx loop with the ability to blend (like the EHX Switchblade Pro) to keep the dry signal mixed with everything else.