i just asked about the Tavor, it is switchable, but you have to buy a new left handed botl carrier, so not exactly a speed swap.
i like down eject, down leave your boy parts swinging in the breeze and i see no problem, that what belt are for. if you can't handle stepping on a few casings, then i guess a few pebbles or broken glass in a parking lot is a problem too?
If it's an issue of damaging reloadable brass, i guess get a catcher?
I guess, personally, though i have limited experience, i like bottom eject. i like it on BPS shotguns, and i like it for bull pups. getting brass in the face is never fun, plus the noise coming out of the ejection port is something i never liked about bull pup conversions i've shot before.
but i'm no expert...