Does the midmount mower and bagger work at least as well as a regular riding mower?
Midmount mower, definitely. Bagger I have no experience with, and my usual advice to people is to buy it without the bagger and use it for a while to see if you really need a bagger. The bagger is expensive and cumbersome. On my lawn, I just use the side discharge (no mulching kit), and I just discharge to the centre, and re-mow over it each round. When I get to the centre there's a small pile left, most has gone into the lawn. I have a chain on the side discharge flap, so I pull it up and drive over the grass that's left, it blows up into the wind, and is gone. It also means less fertilizer on the lawn.
I've never felt the need to bag - to be fair I intensely dislike bagging, so I may not be the most unbiased person around. I suspect a lot of views on this revolve around how thick your grass is, how fast it grows, how often you mow, and how fussy you are. Our grass is a buffalo grass of sorts (kikuyu), it grows fast in spring/summer, but I mow twice a week at peak times, and my main concern is that grass clippings not come inside on feet, which they don't. I'd rather mow more often without bagging (I like driving my tractor, I hate emptying grass clippings), you may be different. But you can try without, and if you don't like it on your lawn with your grass etc, then you can buy a bagger at that point.
If it weren't for the stall cleaning, then a Kubota diesel zero turn, or second hand F, would be the best mower. A BX is a good mower, and not having to clean out stalls is definitely worth a little compromise on mow quality and speed.