I've used one of the Willwood adjustable valves, and you have to fiddle with them a bit to get the right adjustment dialed-in, but they work well.
However, the adjustment setting for an empty truck is not the same as if the truck was loaded with a thousand pounds in the bed.
The Willwood products were mainly designed around passenger/sports car vehicle use, in which the weight on the rear wheels doesn't vary all that much,, if your truck is used a lot between being empty and having heavy loads, you need to aware that brake performance will change,, that's why that lever-linkage valve under the beds for the rear brakes was installed in a lot of our trucks, to vary the rears according to load.
Also, they still have some misconceptions in their descriptions for residual valves;
A 10 pound valve does a good job of keeping the wheel cylinder cups expanded in the rear drums,, but it does not keep the return spring from fully retracting the pistons, the return springs have more than enough tension to completely retract the shoes/pistons.
And, the 2 pound residual valves are for use when the master cylinder is below the disc calipers, to prevent drainback of fluid from the caliper,, with our trucks the master is well above the calipers and you don't need to install separate residuals for the front discs.