*If He puts the BX25 front rims on a BX23 He will no longer be able to use R1s on the BX23 .The total diameter and gear ratio result is the same.
*Kubota went to a "low profile" look on the BXs a few years back, with larger wheels, but lower profile tires, so it all comes out in the wash.
*Both are the same width 8.50.*The extra width might be an issue for MMM anti-scalpe wheel clearance, otherwise, I don't see any issues.