Free service but dealing with a bit of extra mail doesn't sound too bad to me.
It is not a case of dealing with mail.. It is them selling a competing product to your clients; taking premium dollars out of their pocket that you could be getting commission on. Or even worse, another IMO gets your client list and sends their agents by to replace your business.
I learned long ago, the fewer people that have access to your client list, the better.. That includes companies, IMOs etc. I have seen IMOs, General Agents, and even companies send in-house agents into an independent agent's house to write additional business or even replace what is in force. I will never again place all my business where one third party has access to it.