Hi,
Motion Symphony will not contain any of the functionality of Strider so you won’t be making a double purchase if you get Strider now and Motion Symphony later.
They are designed to work together with synergy but are not in any way dependent on each other. Strider and Motion Symphony are intended to be very modular like tools in a tool-bag which can be pieced together anyway you like / any way that makes sense. I am designing everything to avoid a monolithic, interdependent rigid system.