I've used it a few times now (got reimbursed for the fee as a benefit with my AMEX Platinum card). It is very convenient-no lines upon arrival, you don't have to fill out the blue customs form, but in all cases, I've never arrived in the city of my final destination. I was the first at the baggage belt, and even though my bags are some of the first out because of my elite status or cabin of travel, by the time the bags do arrive, most of the people from my flight have already made it through the normal lines. This has been the case when I've arrived in EWR
. Exit from the customs hall is quicker, though, since there is a dedicated line in some airports. Then there is baggage recheck and a second security screening so I can make my connecting flight home.
If you're flying home nonstop and have carry on bags only, it is a no-brainer. If you are making a connection and you don't have elite status that will get your bags out on the carousel sooner than the other pax, the time savings is negligible.
One good thing, however, is that if you're a member of Global Entry, you can register your status in your Frequent Flyer account and for some domestic flights at certain airports, the TSA
will recognize your Global Entry status and you can participate in their Pre√ program which will make security screening much less of a hassle.