The Electro 3 does have a transpose feature, but it requires a few button presses. I happened to download a copy of the manual because I'm in the market for the 3HP.
Use the System menu to transpose:
- Hold Shift and the System button.
- Select Transpose function with the Up/Down buttons.
- Change the tuning up/down by half steps by pressing and holding Shift and the Up or Down button.
I think you have to manually undo that to get back to 0 transpose for the next number.
I don't like the transpose feature because I usually forget to switch back and because real pianos and organs don't have one.
That being said, I disagree with the logic that pro board = no transpose. Professionals are more likely to unexpectedly be asked to play a tune in a strange key to match the singer's range, and even the best players may have trouble going down a flatted third on the fly, so why not make it easy from the control panel?