Absolutely outrageous infringement of my rights. So, I will not use the Square device or accept any client who does. I will boycott it and tell all my clients to avoid it.
This is use of legalese weasel words just like they did to pass the CT gun laws. The Constitution says keep and bear arms shall not be infringed upon. The Constitution says nothing about prevention of the acquisition firearms. (I hear the weasels shrieking this in CT)
The way I see it, they're not really a party to the sale transaction, so they're overstepping their bounds when they try to make a rule like this. Target has a right to tell you that you can't go armed into their store, and you have a right not to shop there. These guys are trying to regulate what goes on that doesn't affect them in any way, so my thinking would be to just ignore them and pretend they're aware of what is and is not their business.