I remember a few years ago being attacked on my argument that using 2 items at the same time with the two mouse buttons was not a good idea, and it would become much confusing.  I think I suggested to use the right mouse button as a "item special function" button: you could use it for doing different type of attacks with a sword for example (like a much slower but more powerful attack), to switch ammunition type if you are using a gun, or anything that could be useful for the item. You could also use it to trigger the shield while holding the sword if you have a shield in your inventory (not sure about this one since is some kind of exception, but it could be useful).
However already using it for throwing stuff is a much better improvement.

Overall I am happy that you decided to make the switch, i do believe controls are going to be much more natural now!

Ps (nobody will remember me, Im just an old fan of the project still lurking and keeping under my radar from time to time... keep up the work guys, you are amazing!)