They might not know that a Roadster is a Rocket III. Ask them again but leave out the Roadster name.
I can recommend the Young Guns Corbin, I like the seat position and quality. But when they say it will take 5,000 miles to break in ... they mean it. Corbins are very, very firm seats ... but very good for long rides. I hated the seat when I first got it, loved the way it looked but it was hard as a rock. But I switched it back and forth with the gell and stock seats for awhile and it grew on me. It's not a good passenger seat, but that was solved with a Butty-Buddy for the wife. I've got around 9,000 miles on the seat now and It's all I use anymore, sold the gell because it just wasn't comfortable on long rides ... made my ars hot and stinging after an hour. The Corbin stays firm, cool and keeps my butt from going to sleep.
You really just have to try things out, but if you try a Corbin ... give it a chance to grow on you and break in.