Is it helpful to use "invention submission companies" to ensure the securing of a patent? What other services might they provide?
A very direct answer to the question is that these companies are not allowed to actually provide patenting services in the U.S. It can only be done by a registered practitioner with a direct relationship with the applicant. Also practitioners are not allowed to split fees with non-practioners.
Some invention submission companies used to commit to the client to provide the services, take their money, and sub-contract the work to patent agents and patent attorneys. This has been curtailed by changes in the rules. See federal register. It is now clear that invention promotion companies can only refer clients to registered practitioners who then have a direct client relationship.
One thing you will see there are the statistics these companies are required to provided - you might have to ask for the data. One data point is the % of clients that ultimately make more money with their help than they spend on the help. Also, since some new rules went in place about four years ago they are not supposed to say they offer patenting services. The most they should do is refer you to a registered practitioner. In theory these companies earn your fees for market research, virtual or real prototype creation and introducing your idea to potential licenses or manufactures.
Find a local non-profit inventors club to get input from others that have been throughout this. You can find them via the UIA ( a non profit ).
I have no direct information on any company in this industry and addressing specific companies is off topic, I believe.