Martin, my ex gf and I tried strap on on 4 or 5 occasions. each time, I had light "milking" or drain coming from my stiff penis most of the time for the first 3 or 4 minutes - it was not a traditional orgasm, but I was draining
My GF enjoyed the action of the strap on against her clit. I had to make her cum with my tongue/mouth before she would strap me from behind, so once she way already "in the zone", she would often climax again while fucking me.
this is probably not the normal experience, but it occurs