Hi James
If you want Ketron sounds, get the SD2 as it has pretty much every sound of Ketron you should need. (If you need external editing then go for the SD4)
If you don’t mind using a Laptop or other computer, then try Livestyler Arranger software, as this gives you pretty much all you get in a standard arranger. (With the addition of VST Support)
I personally wouldn’t go back to a separates software system, (The fully integrated Wersi system is much more preferable) but as you are still suspicious of software arrangers/organs it may be a good alternative for you.
Regards

Bill