I had one good experience and two very bad experiences. The good one, the wrecker was out in short order and fixed my tire. I was in a metropolitan area and not during a holiday, this was also several years ago.
In the last two years we had a flat and a blowout. Both times, after waiting for several hours and calling repeatedly to GSRA, we ultimately called a wrecker ourselves and got fixed up in short order. My understanding of the issue is that the tow companies make more without dealing with GSRA, they do not have many relationships outside metro areas and are typically low priority calls. In the end we did not renew and just have ERS through our insurance company. The allows us to call who we want to get immediate service. You will have to pay up front and submit later but I would rather be in the road than stuck on the side of one. My personal opinion is that it not worth it, they do not provide the service they claim in most cases and are not reliable in your times of need.