I had a Signature on a 2 wheeler and, for me, it was much better than that stock seat. As I understand it, the Sig is the same as a Sundowner plus the driver backrest.
If it is cheap enough, buy it, try it and if you don't like it, you can resell it and probably get most of your money back.
Another thought is to try a demo from a dealer and buy the used one if you like the demo.
Good luck!
I got the sundowner seat for my Freewheeler when my GF found the seat width on the original seat didn't match the width of her rear end. It made all the difference. So match rear widths to the seat.