Going over the Hotchkiss 25mm AA gun it seems to be pretty ideal. Smaller than the MK101, lighter, and with similar overall performance (though lower cyclic rate), it might well be just able to fit in the ME109 motor cannon mount in the way the MK103M was supposed to. With APCR ammo it would be somewhat worse than the MK103 in AP, but would have much better AP than the 20mm cannon and better behind the armor effects and probably require only one. PLUS it would be a long range, highly effective bomber killing weapon for the Me109 to be able to fire outside the range of return fire of B17s, as it had a higher muzzle velocity than the MG151/20.