maybe in the hills of sw iowa, they don't work well. idk.   there are several in our area, while I would be lying to say that they are good as a finger meter, they are almost as good as any vac meter, if they are properly tuned up. and if the operator wants to take the time to set things properly.              I hear what you are saying about a 15' tube and agree, there is inherently going to be some problems with that, no doubt about it. but brush settings, air pressure, speed, trueness of the drum, drum to firewall square, drum to manifold clearances, cutoff wheel alignment, drum gasket, hopper gasket, air leaks,  all have  bearing on how they will perform,   they will still plant with some of these things not right, but not real good.