Had the B&M kit installed in the Aerostar last summer. It prevents complete drain of the pan because it sticks up maybe 3/8 inch, but does allows me to get about 3.3 qts out our 1/3 the total tranny capacity. The shop dropped the pan, changed the filter, installed the plug kit, and installed about 4 qts Redline tranny fluid (that I brought in). I drive it a couple hundred miles, drained the pan and refilled with more Redline. So now it has about 60% or so of Redline. Now I will probably do that every 10,000 miles and periodically do the filter. My understanding is the filter can go 50 or 60 thousand miles, but by doing the fluid exchanges frequently it should make the tranny last the life of the vehicle.
Bottom line: I really like the plug kit and may get one installed on my other Auto tranny vehicle.