I first was trained on interior "reconditioning" products in the early 70s. The SEM product is professional grade, and applied to a properly prepared substrate will last years - 5 or more potentially depending on UV, ozone, and contact with interior dressings (Armor All, etc). It is even resistant to scratches, and can be easily touched up by lightly scuffing and reapplying.
As with any coating (it is a coating, not a dye in the true sense) it is all about prep. The prior post showing all the nifty SEM product actually omits the vinyl/leather prep cleaner, which I use on all substrates. You can start with SEM soap or get comparable results with Simple Green Industrial. (I like Simple Green wipes that come pre-moistened in a pull up container, super strong weave with a smooth side and a nubby side, and make great underside detailing wipes as well.) Then it depends on the piece I'm doing which products I use. I was taught NOT to scuff the substrate unless a repair (polyethelene sticks and welding kits from Urethane Supply Company - work great on interior plastics) was being performed. Not only does this preserve grain, but eliminates releasing any new contaminants from below the surface, or creating micro valleys where crap can hide. Anyway, the Simple Green cleaning followed by the Vinyl/leather prep cleaner, 99% of the time makes adequate prep. THe piece should look chalky and gloss free before applying the coating. I mist on a couple ultra light coats over a 10 minute period at 70 - 75F. Don't do this in a cold shop or you may waste the effort. It takes a little heat (air AND part up to temperature) for this to flash properly. Once the mist coats flash, two full coverage coats 15 minutes apart usually does it.
BTW, I like the Landau Black color for the E body interior. It has a satin gloss that is just right to my eye.
