I personally don’t think that using an amp designed for electric guitars (which are meant to add tone to a minimally complex signal) are the best choice for acoustically complex instruments (e.g. melodica, violin, accordion, etc).
I personally use the Fender Acoustasonic, and find it the most simple, appropriate, and portable solution. I love the sound of my Vibrandoneon through it. Limited combinations of built in reverb and delay, but there’s one that I’m perfectly happy with and eliminates my need for stomp boxes and twiddling.
I use the Acoustasonic head with a workingman 10 cabinet, but this head is hard to find. Scoop one up if you see one on EBay.
Fender also makes an all-in-one acoustasonic line which I’d think is nice.