With hex drivers (especially the tiny sizes we're dealing with) you want a good tool. A warranty is great for replacing your tools, but if they're made of a soft metal they'll round out your screws and you'll be drilling them out. After trying a few different ones I've actually been using this set (from Harbor Freight) and they work great haven't rounded a screw yet.
http://www.harborfreight.com/33-piec...set-93916.html