I was first introduced to these LeadCheck swabs at my Iowa Lead-Safe Renovator class. They provide a reliable test in a simple, easy-to-use format that works well for small contractors like me.
It's nice to be able to show a customer on-site what the results of the test are, without waiting for a lengthy and expensive lab test to come back.
One small problem I did find was that after I "crush" the contents and shake it, I sometimes have to squeeze the tube a bit to get the mixture to flow out. The little plastic pieces from the vials seem to plug the hole a little.
Other than that, they work very nicely and are easy to just toss in the toolbox and go.