Are there any advantages that it has over the wand incarnate?
JW~!
1) It is actually on an useful ego.
This. My wand ego stays happy and is never actually used. I talk to her now and then and hope I get lucky and get free blessings or mp recovery. An ego bow actually serves a useful purpose, with the incarnate skill just an extra benefit. A wand ego would just be an incredibly expensive place to throw craploads of money away... all for a flashy looking incarnate attack that won't compare to your spells/smash/wm/whatever it is you do.