Uncle Dave,
I do know they have dedicated organs but have you seen an Arranger Keyboard with 'tonewheels'sound that can compete with B4 ? ..... I have not !
The Leslie of B4 is not a simple combination of frequency- volume- and phase- (doppler) modulation but all others ARE !
B4 lets you think you are IN the speaker cabinet and the smell of Hammond oil is there again

Roel