There are more than 1000 Mobile Virtual Network Operators in the world. Any brand can go about setting one up, and the primary purpose for doing so is to get a community of people together for a common reason. On the basis of the underlying bearer technology being provided by a large Mobile Network Operator, there is no real competitive advantage to the usual suspects like coverage or speed.
So the competition comes down to what devices you offer, what your brand is (and what else you can offer as part of a broader ecosystem), and how your deal with your customers. Cost-to-serve is a vital corporate metric in an environment that has to be cost-conscious in order to be competitive.
Getting visibility and control over this typically unpredictable parameter really helps in planning the business. Using a service that gives flexibility on the channels offered to the end customer also ensures that the service is carried out in a cost-effective way, typically encouraging use of the lower-cost, scalable channels such as web.