I prefer to work for a smaller staffing agency such as MTC so this is really not anything negative for me, but that could be a con for someone else.
With a smaller agency, I think the attention to each employee is more attractive. However because this company is smaller, I have less colleagues in my district who also work for MTC. This has not interfered with me getting any support I need. In fact, I have my fellow SLPs from MTC numbers in my cell and call them whenever I need. Additionally my district has wonderful mentorship for all employees. You would need to assess the level of support you need in your placement and whether you will need extra mentorship from anyone outside your district.