If you already have decided to have a lot of slices, Merriman's division into 10 equally weighted stock slices and 5 equally weighted bond slices is pretty elegant. It makes a lot of nice round numbers for stock/bond percentages that are multiples of ten, and is especially nice for 50-75% stocks which seems to be a favored range. I am not sure if Merriman's choices for each of those slices is necessarily the best, but no matter.
However, it does raise the question of how beneficial can all of those slices be? It is like rolling a clock down a hill: how many hours can point up at the same time? Just a "12" could make for a pretty lumpy ride. A 12, 4, and 8 can make things a lot smoother. Once you have 2, 4, 6, 8, 10, and 12 though you are getting to the point where adding more hours will be at best marginally useful, but will take a lot more of your time and also quite likely extra fees.