I am happily listening to some mk1 Compass speakers at the moment. I really like them and appreciate their un-fussy nature re amplification and placement. Although when new they are not far behind the price of Arcs, 2nd hand they are usually quite a bit cheaper.
The plus/minus with the Arc is probably its passive bass radiator. Its a positive because, coupled with the Arcs more extensive array of drivers, it gives the Arc more scale BUT in my experience PBR's do demand more thought being given to amplification. Compass's do not so seem to be so choosy about amplification.