These are great. I just tried it on my latest order of 150 boards.
You will get missing numbers. My boards were panelized to 5 boards per panel, and for the batch of 150 boards (30 panels), 30 serial numbers are missing. So, instead of getting 0200-0349, I got 0200-0379 with 30 boards (6 panels) missing.
Not a lot you can do about that I suspect. Would be great if they could test the boards prior to screen-printing, but... whatever. I just need to keep a record of board serials I never received.