If you want to keep cleaning your suspension after each ride or hear them squaking during a ride than don't buy any but for the cost, it's worth it. At least with the shock covers, you just have to rinse them off and you're done.
Dude they are a hug plus. They save your shocks from getting all caked with mud and dirt. I have never had any problems with any of my past bikes with these covers on.
I got mine direct from the maker in Canada. They make most of the covers for the companies who retail them out. They were awesome to work with as well. I even sent them there first pics of a trx with the skull covers on them since they didn't have them. http://www.shockpros.com