Good question. I too would like to invest in a Lester G for the organ effects. The Hammond organs on the Genos are sketchy at best - as is the vocal harmonizer - but that's another topic.
I would choose the Lester G (G is for guitar) instead of the Lester K (K is for keyboard) because, with the Lester G, you can vary the rate at which the Leslie engages. I don't know why they wouldn't put that feature in the Lester K instead of the Lester G???