I went from a BX2350 to a B2601. It is a lot of difference.
The BX is a tractor that is basically built to the footprint of a ride on. It's low, and it's compromised by that. Yes, the B is basically teh same HP and basically the same width/length. But the 3ph is a lot more capable, and the loader a fair bit more capable. It has a 3 speed gearbox, and is quite a bit faster. It has a lot more clearance, and the larger tires (particularly in the front) make it more comfortable and you're less at risk of squishing the front tires with a heavy load in the FEL.
I have been really happy with the upgrade.
But, others are correct that it's really not a lot more money to go to an L2502 (or L2501 if used), and it is a lot more tractor. If you're not mowing, and need to lift or move a decent weight, then the L is where to go. If you are space constrained, need to trailer it, can't park an L in your shed, or you need a mid-PTO, then the B is a good size machine and in my opinion is quite a lot more than a BX. The ergonomics on the B to my mind are better, particularly the loader stick. But it's hard to go past the amount of metal you get for you money in an L.