I think that you have the attachment design accurately described.
I would characterize the PT approach to design as "KISS", which makes the attachments lightweight, inexpensive, repairs easy, and generally quick. Pump replacement on the engine would be a definite exception, but not worse than skid steer repairs.
Yes, brush cutters are always a flying debris for any machine. I brush cut with a logging helmet with a wire mesh face shield. I have never been hit with anything more than a ricochet twig, but I don't want to push my luck. The set up of the PT brush mowers is such that under normal operation the flying debris tends to go forward or under the tractor if the mower is on the ground. I don't brush cut near people or buildings. I think that there was someone here that did polycarbonate front shield and someone who did a woven wire mesh one, but that is just from memory. I.e. not common.
All the best,
Peter