Other than being insanely loud and dusty, I love the billy goat lawn vacs.. especially for oak leaves. Most other leaves, once they are dry ar epretty easy to just obliterate with the mulch kit but oak leaves don't budge, or get chopped up much. The same holds true for oak leaves in the billy goat, it sucks them up just fine, they just aren't going to be reduced down in size as much. The newer models are much easier to adjust; move the main nuzzle higher or lower to the ground.
On properties you maintain on a regular schedule, it might take an extra pass or going slower, but it still sucks the leaves right up. On properties where they have been neglected and really compressed into the SA grass, sometimes it easier/faster to blow them to a hard surface then suck them right now.
The billy goat has made our leaf clean up so much faster, it has really helped us sell the yearly contracts. When people ask what they are getting for their money in the winter months, the leaf clean up is part of it and now is almost effortless. As the mowing turns to every other or every three weeks, we have a separate trailer ( our old open trailer) with just two billy goats and some higher sides to hold in the leaves. We just dump/compost what we collect back at our house.