I've heard of it - seen it mentioned in messages from a few other trailer owners. No pros or cons. If somebody is using that brand and not complaining, that could be a good thing? Google 'greenball towmaster' and you will find a number of comments and I have yet to see a negative.
Former owner of 2004 American Tradition and several other RVs
Home is in the Ocala Nat'l Forest near Ocala, FL
Summers in Black Mountain, NC