tl;dr: I always welcome constructive criticism.
I once sent some unsolicited beta'ing, including grammar and typo corrections and some suggestions for phrasing, to a fanfic author whose work I enjoyed. His/her stinging rebuke of my presumption made me aware that not everyone welcomes criticism, however constructive or well-intentioned it may be. I admit that up until that point I had thought that all writers would welcome suggestions they might use to make their work better. For me, it feels pretty neat that someone cared enough to spend their own time going through my work with a fine-toothed comb, though I suppose to others it might feel like nitpicking.
My translation process goes like this:
rough draft > re-write / research > glossary construction / linking > upload to website > final read-through > publish
Sometimes, I might go through one of those processes faster than I should. Last weekend, a family friend who had recently taken up (academic) translation insisted on reading one of my translations. After gently trying to dissuade her, I shrugged internally and gave her "Rebels of the River-Edge: Prologue." I think, despite reassurances to the contrary, that she was expecting "The Tale of Genji." She handed it back without a word. Through no fault of its own, I'm still cringing a little when I go back to that translation because the awkwardness of that interaction still haunts me--which probably led to a less thorough last read-through than usual.
All this to say that nobody's work is perfect, and my stance on constructive criticism remains unchanged: yes please!