I wish that stuff was only 3" material, Island. Some of it is, and some of it is smaller and some of it is larger.
A $2000 flail mower like your Caroni TM1900 wouldn't do anything to the poplar, aspen and growing oaks. A flail mower is made to cut small brush, rough grass and with finishing hammer, as a finishing mower on golf courses, parks and so forth. A three point forest mulcher,
like a Seppi Miniforest, an attachment that would only work on this material when driven backwards also quotes out at $27,000 plus tax, plus replacement teeth and Mike over at Titan Machinery would love to sell me the one they have in stock. This is to say, Island, I'm using the cost effective system and it works fine on material approaching five inches.
At any-rate, in the video I note that I'm happy to cut small stuff at the beginning because most of the time I'm running into 20' and taller material like I'm processing at the end of the video.