SEM is a great product. If you are going from any color to black, you will be fine, and the good deal is you can rattle can if you like, but I recommend buying it in a half quart and squirting it with a detail gun. It goes on fantastic. The only thing I can say regarding how well it will last is that those buddy seats take a heck of a lot of wear, rubbing against the seats every time it's lowered and raised. If it's on a weekend cruiser, you will be good. Daily driver, hmmmmm. Here's my recipe.

Do this on a warm day. let the vinyl get warm.
Clean it with POR Marine Clean, scrubbing with a green 3m pad. The stuff will clean the spots off a leopard.
Let it dry completely.
Shoot with SEM Surface Prep so the surface becomes noticeably "Wet".
IMMEDIATELY follow up with a fog coat of Color Coat.
Follow up with 2 more coats at 5-10 minute intervals.

You'll be amazed how well you can still see the grain in the vinyl. The stuff is great.