That mower that you are using is doing a really nice job in my opinion, a cleaner looking finish than a rotary cutter.
I have a few banks to mow, and it's great for that, but I bought it mainly so I could offset it and not run over what I was about to mow with the tractor. With a rotary I got a lot of "popup" from what wasn't cut when the tires crushed stuff down before mowing. Also, the rotary left big windrows rather than spread everything evenly like the flail does. So yes, it's generally a much better cut than the rotary.
When I have to run over un-cut growth the flail does not do a great job of cutting what the tires have run over; not noticeably better than the rotary did.
Even running offset, with growth as heavy as you see in the first two photos, it does in places leave some of the grass six to eight inches long, I suppose because it gets pushed down with the front of the mower and doesn't pop up enough to get cut correctly.
It's worse in the fall when I have some pretty stiff weeds in with grass three feet tall and more -- some of them are left a foot or more tall. It was very bad with the factory front guard made from heavy belting. Now that I've replaced that with a chain guard it's much less of an issue.
I've got the tractor tires set as wide as possible because of the hillsides, so I often don't get to use the full width of the mower while keeping the tires off the un-cut material. That's especially true when I'm on the down-hill side as in the last photo, as the rig crabs as much as a foot down the hill. But on the up-hill side I have to be careful to keep the front tire a foot or so away from the standing material or the crab pulls the mower too far down hill and leaves an un-cut strip.
