Question for the high rounders: How exactly does O.S.C.A.R. work after Round 50? How manageable is he?

I know that he drops his patrol shtick, begins constantly pursuing you, and moves faster. Seen lots of complaints that this ruins the map after Round 50, but some say it adds a fun challenge.

Does he respawn every round? How difficult s he to kill with fully upgraded weapons? Any good strategies to deal with O.S.C.A.R.?