Just chiming in here to add that we used them to 1) fly into the US, and 2) board Royal Caribbean's Wonder of the Seas.
They were really inexpensive, easy to book, great to deal with, and our results came via email the exact minute our appointment was completed. I liked being able to book both my husband and I into a single appointment, to save money & time.
We used the green/free tests that we get here in BC.