I use a 3-light receptacle tester all the time as part of the final room by room receptacle check out on new finish wiring. They make it a lot faster and easier to check the TR receptacles required for new and remodel work.
Granted they are not a comprehensive tester, but because they are so handy, that I often find myself using them for initial troubleshooting on a service call before getting out my meter and removing a receptacle and then also again to verify my work after replacing a receptacle.
