I’m curious about the connotation with this. Is this sort of like, a positive thing but also saying someone is a bit of an oddball? I take it it’s not saying the person has a good sense of humor but is saying, rather, that the person is a bit odd themselves?
First, ‘welch (ein)’ is a bit outdated, for being entitled to say this (with serious intentions) you at least have to wear suit, moustache and a homburg, otherwise it’s not appropriate unless you say it ironically to mock such a person.
Other than that, it is something you’d only say about someone you consider a bit odd, not as a compliment. Generally, ‘komisch’ is more often used to describe something odd, even unpleasant, than to describe something funny.