Depends
If I have reason to believe alt me is basically just me from a different place, I would certainly go with him. I'm not the type to hop dimensions lightly, nor to have some kind of nefarious purpose for doing so. Now another version of me MIGHT be willing to orchestrate a "sacrifice my twin to save the many" scenario, but I am a bad enough liar that I am far more than likely to spot that kind of deception.
If otherwise, it gets more complex, but chances are good I will go. Dimension hopping capability would appear to indicate that this individual and the society he comes from is significantly more advanced, and frankly more interesting, than ours. Some questions are in order of course.