I have the marware relay for the 1st/2nd gen nano and while it does its job, it does have some issues.
First, I only use it for running, so it's in and out of the case once per day. The area where the nano is inserted is beginning to wear and fray after 3 months of use. Another few months and it will be totally unusable.
Second, it does nothing to protect the nano from moisture. I guess it is made from neoprene. I always remove the nano straight after my morning run and it is pretty slick and damp from sweat. I've had to use tape to seal my nano from moisture because it quit working for a few days, I'm assuming from being wet.
I'm looking to get a 3G Nano soon, but based on experience, I'm going to try to find something other than the marware for my nike + runs.