There is a specific thread devoted to ramps here in TB, started by Brian R. Tyler. Lots of information. In addition to Willis, a lot of other "technical" players are using ramps: Richard Bona, Hadrien Feraud, Matt Garrison, Janek Gwizdala (Willis created the concept and the name)...
I have practiced the three finger technique. I don't get the open position, but the closed position feels very natural to me. At the moment I have installed ramps in most of my basses, and I play with closed position or combinations of thumb and index-middle-ring for string crossing. Playing with the ramp and three fingers helps me in having a light, even, precise touch, with less hand movement, more articulate sound, better muting of unused strings. It wont't make you a genius or double your speed. It's like running with lighter shoes of better quality than usual.
I have studied The Fingerboard Harmony (FBH) Method by Willis (Book-CD). It's clear and concise. If you are a intermediate player used to playing funk, rock, fusion but get lost playing through changes, the method will help you in putting yourself together in a short period.
Willis is not a frustrated player that only teaches to make ends meet. He enjoys teaching and sharing knowledge. Just browse his Ask Willis section in his site and in Bass Musician Magazine Online.
I wouldn't ask for private lessons without studying FBH and watching his video first. I would ask for the advanced stuff that can be best shown face to face. Just my opinion.