I have that backrest. Actually, that backrest in particular since that's a picture of my bike! Grasshopper Limited makes it (Dakals, on this site). He also made mine for my C50T. It is a heckuva well made product and a great value.
Installation takes all of 5 minutes: remove pillion, remove driver seat bolt, install backrest bracket (or "sleeve") and re-install bolt and pillion. Done. The backrest slides into the "sleeve" of the bracket. The bracket is not visible when the backrest is not installed. Backrest also fits easily into the stock hardbags with plenty of room to spare.
No, it's not adjustable, but it is large enough that it's going to hit 99% of riders right where it needs to: in the lower back for that support.
FWIW, I can attest to Lonnie's product and his dedication to fellow m/c riders, being one himself. And no, I don't have any financial ties or incentives tied to this product. It's just a darn good product at (finally) an affordable price. Made by a rider for riders.
Best,
Daryl