I've used Smith & Co's CPES and two-part filler. At least in the shop, both have performed as advertised and appear to be excellent products. The wood filler has better qualities than any epoxy/microballoon mix that I've used. It applies easier, takes a feather edge, dries stronger and less brittle but also has more flexibility. It sands well, but not quite as easily as epoxy microballon mix. Plus you don't have to deal with breathing the dust from the microballoons when you mix it up.
Have any of you tried Smith's other products? I'm especially interested in their Tropical Wood Glue, which they tout as an epoxy suitable for "difficult" woods like teak, oak and other oily woods.