I use multiple coats of Sally Hansen Double Duty and have been for years with no problems. I always have it on and if it peels off, I replace it immediately. I think that any product that promises "maximum growth" or anything like that is b.s..
2013 Jeff Medlin '37 Hauser 640mm sp
2006 Michele Della Giustina Concert 10 string 650mm ce
2005 Jose Ramirez 4E 650mm ce
2005 Manuel Rodriguez Model C3F 650mm sp
2003 Manuel Rodriguez Model D 650mm ce