I know a 6 year boy old called Izzy. Not short for anything. His parents are both creatives. As far as I'm awear he doesn't get teased for it. Isadore is a great name, and is cute with Otto and Evan!
not pretentious, but most boys would be embarrassed to have such a feminine sounding name.
I'm not sure I would have said embarrassed but I would say it's not easy name for a guy. With the overwhelming popularity of Isabella and her derivatives I fear that non-name-efficianatos would assume he's a girl. I can see this being particularly trying during adolescence.
Personally I think Isidore is a rather handsome name but would do better a MN or GP and not a FN.