We’ve used them three times now.
The first two times weren’t emergencies, so we scheduled visits the next day, and each time the technician would call and give us a 30 minutes heads up on arrival, and always within the allotted time frame we were told to expect them.
When we did have an issue that needed to be fixed asap, while another company told us to wait until next week (what?! right?) Jenni Plumber said they were sure they could send someone later that day, and they did, of course with a call letting us know someone was coming.
This, and the wonderful receptionist service on the phone, make dealing with them so much more pleasant.
As for the plumbers themselves, they were always very nice and courteous and were very knowledgeable about what the problems were, possible solutions, as well as just information on how things work (always curious, so was bombarding them with questions.)
I could not recommend Jenni Plumber more to another person.