I also have yet to see an aftermarket MC with the residual valves installed.
A few years back when I spoke to MP Brakes about the absence of them in their MCs I was told that the residual valves are not absolutely necessary but they are recommended and to
not use them at my own discretion.
The problem with the aftermarket MCs is that they are not machined to accommodate the factory type residual valves, at least the ones I have seen. So, one option is to add the inline residual valves.
I did not want to go with the inline valves so I took a chance, hoping there was enough material in the aftermarket casting to allow for machining. Fortunately, there was and it worked out well for me.
Dave