TripKey is a relatively new transit pass that I found to be very useful during my recent week in Amsterdam. We did have a bit of a wait at Hertz, which is where it is picked up at Schiphol (there are other locations in Amsterdam) as renting cars can take some time, but once we gave the agent my confirmation code, she was able to give me the two passes, although she did seem a bit unfamiliar with the process. On our return, we had no wait, and the agent took the passes and told me I'd get am email confirming the return--which arrived just as I was leaving the counter. We used the cards on trams and on trains to get to Schiphol (for the Keukenhof bus), and to Haarlem and Delft. Worked beautifully.
The only small wrinkle was that I had made an error in my husband's name when registering him, and didn't catch it until I had clicked "next" to pay his 3.50 euros. There was no way to go back to correct information, and when I tried to start again, I was told that the email was already in use. I emailed support to see what to do, and received a prompt reply that I could get two cards--which is what I did. There was a bit of confusion after I returned home about whether he had used a card, but that was quickly cleared up--customer support responds promptly to emails.
All in all, I was very pleased and would certainly use it again.