I have not used one in this application. You want at least 60 amp capacity unit. --(probably in reality 100 amps better because you need to be able to briefly supply locked rotor capacity current). bypass unless you are using it in the last few feet. I use short bursts of the Up switch. You are working thru relays--with most of the switches-
I would put the control unit after the relay and have a bypass switch (which has to also be able to handle the load). How much current draw will there be as you drop the voltage to get the motor moving when under load? (of course these are all relatively small motors geared down, so there is some inertia in the system.)
Let us know how it works out. I see where people have talked about doing it, but no place where it was done.
If you went before the relay, I would fear relay burn out, from rapid open and closing of contacts.