If you use two blues in a 3-way, then you can bind them together somewhat like Zwave association. (The wiring diagram page you referred to is a work in progress and doesn’t yet contain those instructions.) If you do that, you’ll need a hot and neutral in the non-line box, which is usually easy to do via a 3-wire between the switches.
Inovelli is releasing an Aux switch as well. It is not blue-specific.
The Blue switch is pending UL certification, so while Inovelli expects by August, I don’t think anyone can say with certainty.