My Rav says it is not reliable. Just recently a veggie chinese place opened in Queens and there are rave reviews about the food. But it's IKC, as is a 16 Handles Frozen Yogurt place in the Queens Mall (that used to be under Rabbi Mehlman). As far as frozen yogurt places, aside from the concern about employees eating their lunch in the same area, there is also the issue of toppings. For example, the Red Mango in Rego Park will tell you the are kosher because the yogurt packages themselves have a hechsher. However, they do use non-kosher toppings and who's keeping track that the kosher M&M's aren't getting mixed in with the non-kosher whatever. Plus, once the package is openned, the certification is no longer valid in an establishment that is not kosher itself.
BTW, R' Schector no longer gives his hechsher to the Red Mango referred to above.