Steering customers to one Clearinghouse will not cause legal problems. Like any other service or product, people will either go for it or they won't.
This does not mean you can't use the PM feature of the upcoming Amazing Charts. You can use another clearing house. You just won't get any group discounts. ***
***I say this assuming Amazing Charts generates the 837 claims files in a folder where you can upload them to where you wish rather than sending them straight to Gateway EDI.
JamesNT