Definitely worth doing. Beth will pick you up at your hotel and drive you out to the place in the countryside where the horses are. The horses are very friendly and look very neat and healthy.
The ride an the views are spectacular.
You should definitely book the ranch lunch with this trip which is served after the ride at the house of the family that owns the horses. Great hospitality and very good food for a very small price.
A perfect "Mexican" experience in San Miguel that otherwise can be quite touristy (but still very nice).