OK, I made some photos of the two together. I also want to make a video of them running - they run very differently and it's noticeable. It's surprising how much work the B will do at idle, and it's quieter at idle than the BX. In top gear it moves around quickly with quite few revs, the BX always needs a lot of revs to move at any decent speed.
You'll see that my BX2350 is pretty rough - it was that way when I got it and if anything I've probably broken a few more bits of plastic. Mechanically it's sound though, and I think all the BXs are basically the same underneath, it's cosmetic stuff they've changed.
Buckets are level at the front. The B bucket is larger, and of course has two rams for curl.
Lawn is a bit brown where my weed spray that was supposed to be selective (and not kill grass) might have been a bit strong. It didn't kill all the weeds either, so that's a fine balance apparently.
The B is only a little longer, to be honest it feels like more. The measures claim they're the same length, but the B is measured without 3ph, the BX is measured with 3ph, so there's more in it than the measures say.
The tire size is the most noticeable difference - the B tires look almost twice as high. The BX are very wide to make up for their lack of height - they still have quite a bit of footprint on the ground. But small tires make for a rougher ride, and the small tires at the front limit what the FEL can lift a lot. From reading the owner's manual it also seems like non-US markets get larger turf tires than the US market. I guess the size that's used in the USA isn't available in most other countries, so they're using a different size. Or maybe there's another reason.
Tractor shed in the background. I dug out that hillside with a 1.6T Takeuchi excavator I borrowed from my father, and the BX to cart it all away. You can do a lot with a BX. I'll take some photos of each machine in the shed - the B fills the shed a lot more. That might be a good way to see the size difference against a fixed space.
From the front the B also looks quite a bit larger. And of course you can see my BX with no headlights, looks a bit sad.
There's not as much as you'd think in the FEL height. It is quite a bit higher, but really only 200mm/8 inches I'd guess. The BX is just a little low to dump over the side of a standard high sided skip bin, so I expect the B to be an improvement there (not that I've had a skip bin since we finished house renovations).
Finally, there was some comment on the brush guard. It's fixed and doesn't move, unlike the L.