Pretty much any of the usual cons that go with working for a small company.
For me the most annoying thing was the healthcare, it really was a good option for everyone else, but I think I just had bad luck with the HRA. It did let me get the best individual plan available and have my premium be paid for in full, which is more than I can say for anywhere else I've worked. The pros for working for OnWire far outweighed that one small issue.