I did use the Midjay with success. I used a 7-pound controller keyboard. The Midjay has great sounds and can use all the SD1 styles, plus the operating system is very good. It has a hard-disk recorder and lets you play styles, midi files, mp3s and wavs alone or in combination.
Shortcomings were that the vocal harmonizer was strictly a vocoder and I missed the more versatile harmonizer on SD1 and Yamaha.
You can easily search this forum for my previous assessments of these instruments.
Good luck with your choice. It's great that there are so many wonderful options.
DonM