In good hay makes a good dense 1000 to 1500 # roll. will stand up good and shed water well. And you can stop the rolls smaller than 5 ft if you need to. Closed throat means it has a roller that is spring loaded and the force and pressure of the incoming grass pushed the roller up. A very good system for making consistent rolls of hay. The only problem I ever had involved clumps of damp hay say around the edges that would wrap around the throat roller. Most of the time the shear pin shears and you clean it out and replace the bolt. If it doesnt shear it will break something. these baler will make a very good tight roll of hay.
Open throat means anything that hits the pickup teeth goes into the chamber( fence post, wood chunks, scrap metal).
Good balers just dont pay too much and keep em shedded to protect the belts.
Good luck