Unfortunately, this enables vendors to prevent fair-use account sharing, and it looks like to implement some sort of DRM. My team at a small company used SurveyMonkey and only allowed two devices to login, and we paid for only one user license. However, our position was split into two part-time jobs; hence the pricing would have been unfair. I think your service is a good solution, as long as SaaS providers implement more reasonable licensing models.