There have been reports that this is not compatible if you are using a controller instead of K/M setup, as the controller interface does not allow you to select the additional party members that you can recruit. Barter menu has party members portraits going across the top of the screen but they're all still functional and you can click on all of them. You can also very easily just click on the portraits in the sidebar to switch between characters.
It's still completely usable, just the behavior is weird. Character sheet menu is a little wonky if you use the arrows to navigate. However Zlayer has confirmed that dismissing and re-recruiting companions will allow the party size limit to be removed. Note: On existing saves the mod works best without a full party / with no-one yet recruited. I have confirmed that all companions transfer over successfully into Act 2. I've successfully tested out combat, bartering, companion attitude change, full companion quest lines in Act 1, formations, character sheet and inventory menus. I've done initial testing, playing as Fane and adding all the other origin characters in Fort Joy. Initial mod to allow more than 4 followers.