Completely agree with the lock-in, and they aren't the best / featureful device out there. It seems the sweet spot for them is places with LARGE distributed footprints (such as retailers), where you can have very simple networking (some back to HQ, the rest to internet).
It fits well with being able to rapidly bring bodies into a project and implement change X across hundreds of stores, while having a standing IT team of 5.
If you have onsite (fulltime) IT, its likely not the best option.