I had the Tank Slapper kit and thought it a complete waste of time and money. After one year the only pieces that stayed on were the 3M ones and the non-3m one on the top of the tank (the rest fell off one by one in rain storms).
When the tankside pieces went I replace them with Gripsters.
Please note the Gripster is not competition for the mag knight/tankslapper kits.
They are intended primaryly to increase friction at the contact points between your legs and the bike. They are not meant to keep the bike looking good and be invisible. I purchased the "ice" ones and they are very visible on the bike especially after my Aerostich leg zippers scratched them up a bit.
That said, if you've purchased an aftermarket leather seat, the Gripster will keep your reproductive parts safe and make riding more comfortable in general. But the real benefit is with "spirited" riding: if you want to slide around, relax the legs and move all you want. If you want to stay in one place, lightly grip the tank and friction will do the rest. It rocks.
Once you try them you won't go back. For $39.95 you'll get two custom-cut pieces, or for $34.95 you'll get two large sheets you can cut to fit.
Testing was done over 9 months with a 2005 FJR1300, Rick Mayer leather seat, and Aerostitch 1pc roadcrafter on various roads incl Road America. Gripster Ice "General Sheet" was used, cut using TankSlapper backing piece.