I'd try my butt in several before you buy. I have a Mustang Touring with a backrest on my 03 Standard RK and it's great after I broke it in. I also have a Badlander for solo cruising and it just fine.
I was at one HD shop in TX (Corinth?) with a buddy while on a business trip. They had a frame buck that you could try different saddles and bars. Might be wotrh looking for.
You might also use the search function as there are lots of opinions. Might also post an intro in that section.-2$en#e-
I have the Mustang two up touring seat part #75464 with driver's backrest kit on my '04 Road King. It's very comfortable even on the longer (600+ mile) days travelling cross the country. Comfy for the passenger too.
This seat does, however, make you sit a bit higher on the bike. That may be a problem for riders with a shorter inseam. My inseam is 32" and I have no problems touching the ground flat footed at stop lights.
If you're talking about the H-D Sundowner, we had that seat on our Road King. I got it because they were having a 20% off sale at the dealer where I do what little business I do.
While better than stock, if I had it to do over again, I would have sprung for the Mustang. With stock seat, wife was uncomfortable after about 30 - 40 miles. With Sundowner, that increased to about 50 - 60(60 on a real good day). A weekend of riding(300 - 400 miles) and she wouldn't get on bike for a few days.
I've got 18,000 miles on my Mustang 75464 with the HD rider backrest kit. I highly recommend it.
My buddy had the Sundowner on his Road King with the HD rider adjustable backrest. The seat kept ripping from adjusting the backrest. They warrantied 2 of them before they told him to try another seat.
I bought a Badlander for short rides and I was very surprised how comfortable it was. I wouldn't hit a dog in the ass with the stock seat. Sold it on ebay for $75.
I have had both on my RK. For long distance touring comfort the Mustang wins hands down. The Sundowner was much better than stock however, the foam breaks down after 8,000-10,000 miles and then it becomes very uncomfortable on longer rides.
Ditto on the Mustang two-up wide touring seat. It's a great seat and very comfortable. Sitting you up an extra inch may also be a problem for taller riders. I'm 6'3" and have head buffeting now that I did not have before switching seats. I may need to buy an oversize windshield.