I have used Color Plus (
:: Color Plus ::) products but not on a seat, I have only experience with using it on a shifter boot on a 993. I have heard from other guys who have indeed used it on seats and most say the results are incredible.
Now, to the point of how long does it last, I've read mostly good things from guys saying their seats looked good for years, a couple stated it wore of within 6 months.
From my experience, it is all in the preparation. You must go through all the steps of cleaning and moisturizing and then cleaning again and letting it completely dry. My first attempt started flaking within 6 months, I emailed Color Plus, bought their cleaner and soffener (their name) products and used them after stripping off the first attempt. The results were excellent and have held up for nearly a year.
I hated to spend the money but my 993 is a rare Light Grey color and finding a matching shifter boot proved impossible.
Original NIB 993 Shifter in Classic Grey:
Re Dyed to Marble Grey: