I tend to copy/paste into the console anyway during development, so having to copy/paste into Tampermonkey too doesn't slow me down too much. I suppose it would be nice to have a more integrated workflow though.
Yeah, I agree it's not slow as such - but I find it a bit distracting remembering to do it, and if I don't concentrate then I forget and then I risk confusing myself momentarily (not hard to do).