There are several expedited screening and entry programs, they overlap confusingly, and people routinely buy the wrong one.
Working out which applies to your travel takes about ten minutes and saves either money or a great deal of queuing.
What each one actually covers
The distinction that resolves most of the confusion.
Expedited domestic security screening covers the checkpoint before a flight, at participating airports, with a shorter line and reduced requirements to remove shoes, belts and electronics.
Expedited entry on return from abroad covers the immigration and customs process when arriving back in the country, using kiosks or a dedicated lane.
These are different problems. Somebody who flies domestically weekly and never leaves the country needs the first. Somebody who takes two international trips a year and rarely flies domestically needs the second.
The programs covering international entry generally include the domestic screening benefit as well, which is why they are frequently the better value despite costing more.
The application reality
Where people underestimate the effort.
Applications require a background check and, for most programs, an in-person interview.
Interview appointment availability has been a persistent bottleneck, with waits reported in months at busy locations.
Several programs now offer interview on arrival, completing the process when you next return from abroad, which removes the appointment problem entirely and is substantially underused.
Approval is not automatic. Certain criminal history, customs violations and immigration issues result in denial, and the criteria are published.
The cost calculation
Membership runs several years, so the annual cost is modest.
Many travel-oriented credit cards reimburse the application fee as a benefit, which makes it effectively free for cardholders and which a substantial number of eligible people never claim.
Checking whether a card you already hold offers this is worth doing before paying, and the reimbursement generally applies once per membership period.
What the benefit is actually worth
Being honest, because it varies enormously.
At a large busy airport at a peak hour, the time saving is substantial and occasionally the difference between making a flight and not.
At a small airport, or off-peak, the standard line is frequently short and the benefit is marginal.
The expedited lines have also become busier as membership has grown, and at some airports at some times the standard line is faster, which members discover with some irritation.
The more reliable benefit is predictability rather than speed. Knowing roughly how long screening will take allows tighter arrival planning, which is worth more than the minutes saved.
The airline and airport variables
Two things that determine whether you can use it.
Participation is by airline. Booking on a carrier that does not participate means the marking does not appear on the boarding pass and the benefit is unavailable for that flight.
Participation is also by airport and by terminal, and some locations offer the expedited lane only during certain hours.
Which means checking both before relying on it, particularly when flying from smaller airports or on international carriers operating domestic segments.
The reciprocal and international schemes
Worth knowing about for frequent international travellers.
Several countries operate their own expedited entry programs, and some have reciprocal arrangements allowing members of one to use another.
The eligibility, cost and application processes differ, and the arrangements change.
For anybody travelling repeatedly to a specific country, checking whether such a scheme exists there is worthwhile, since the queues at major international arrival halls are frequently the longest part of a journey.
The privacy consideration
Worth stating since it is a genuine trade rather than a formality.
These programs involve providing biographic and biometric information, consenting to background checks, and in most cases fingerprinting.
That information is retained and shared between agencies according to published policies.
Whether that is an acceptable exchange for shorter queues is a personal judgement, and it is worth making deliberately rather than defaulting into.
What I would actually recommend
If you leave the country at all, the program covering international entry is generally the better value since it includes domestic screening.
Check whether a card you hold reimburses the fee before paying.
Use interview on arrival if the appointment wait is long, which it usually is.
And confirm your airline participates before assuming the benefit applies to a specific booking.
Renewal, which people miss
Memberships expire and renewal is not automatic.
Processing has at times taken months, and a lapsed membership means losing the benefit until it is restored.
Most programs allow renewal well before expiry, with the remaining time carried forward, which means applying early costs nothing.
Setting a reminder a year ahead is the practical answer, since the expiry date is not something anybody remembers.
Families and children
Rules on children accompanying an enrolled adult differ between programs and by age, with some allowing young children through the expedited lane and others requiring individual enrolment.
Checking before relying on it avoids the situation of a family splitting at the checkpoint, which is the specific failure worth planning around.