I used Delta Leaf Labs once very recently and took seemingly good samples which is a process that requires grinding the leaves' pigments into small pieces of paper and mailing them to the company. They have since told me my samples were inadequate and so far, one of the results that the lab had made to seem to me to be a confirmed result was wrong. Several other results were inconclusive. $150 wasted as now I am flipping all the plants as I should have done previously. My negative experience with them could have been my fault as I had sprayed my plants with sm-90 and did not have cotyledons from which to take the samples. They recommend not spraying the plants prior to testing and having the customer take samples from cotyldons in their instructions.
I can't think of a time that it would be worth it to send a sample in to a lab to get a sex result that you could confirm yourself for certain within 14 days. Thats about how long the lab results will take when you include placing the lab sample kit order and waiting for them to come in the mail and then taking the samples properly and then sending them back into the lab and then waiting for them to get back to you. In my experience, you are most certainly better off performing the test yourself with a good old fashion flip and check until you either get pistils or nanners. That way you will know the sex for certain and also save about $10 per plant.