Don't know how far back we'd have to rewind the clock in order to be evaluating a relatively healthy Monson, but I saw him in matches against guys like Almeida, Ribeiro, Brandon Vera, Dave Avellan and others during the early 2000s. The majority were GQ matches at Marist High School, but I think I also might have seen him in a match at a Maxercise tournament & in a few matches at a Naga Battle at the Beach ('03 or '04. Whenever they first had an Expert division & it carried a cash prize).
Overall, it was clear he was very hard to turn or sweep, but I don't recall a lot of impressive takedowns. His matches tended to be dull.
Now, in his defense, his reputation sort of preceded him & guys often pulled guard. But, I do recall instances where a few would choose to fight the standup battle with him (Almeida & Avellan come to mind) and would do surprisingly well [given Monson's wrestling credentials].