While I'm thinking about it . . .
The SD7 lets you hold a lead sound, say a Sax, change sounds, say to an organ, and the Sax keeps playing, unchanged until you release the key. You can play the organ sounds with the other fingers or other hand. They can be any sounds, this is just an example. This if very useful.
On all other arrangers that I remember, the change in effects causes an abrupt change in the original sound.
Not sure I'm explaining this right, but I'll try to do a video to illustrate when I get a chance.
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DonM