pto vs non pto.... sickle mowers do not require a large amount of HP compared to a rotatory cutter or fail mower. but more of issue. does the sickle have an hydraulic cylinder for up/down.
that cutting bar can be a bear at times, trying to pull / push up and lock into travel mode. then dropping the cutting bar down into thicker weeds. and walking about in the weeds.
if buying used. double check the cutting bar itself. and the teeth on it and more so for any bending in the cutting portion of the sickle mower. it is not a cheap replacement piece of metal.