Victor,
If you've read anything I've written, you know I'm BLUE to the bone so, I'm happy you're going BLUE. However, looking in my NH brochure I'm showing that the TC18 & 21 are only rated for a 48" Rotary Cutter. You have to move up to the TC25 for a 60" rating. I am using a 60" rear finish mower, Woods, on my TC18 that it is not rated for, the salesman said he had sold several for the TC18 and customer feedback was great. I have used it several times and have no problems except having to add front weights to keep the front end on the ground. I want to add a 48" rotary cutter to my collection of attachments.
I haven't used a rotary cutter before but my neighbor has a 5' one that he said shook his Ford 8N around when he used it on that. He said I could try it if I wanted to but I haven't taken him up on it yet. He currently uses a Flail mower for what most people would probably rotary cut and he really likes it. The TC18 & 21 are rated for 50"/60" Flail Mowers. Good Luck, sorry if I muddied up the waters! You might ask several NH dealers if the smaller TC's will handle it or not? Please let us know. JimBinMI