There is simply no other exercise, and certainly no machine, that produces the level of central nervous system activity, improved balance and coordination, skeletal loading and bone density enhancement, muscular stimulation and growth, connective tissue stress and strength, psychological demand and toughness, and overall systemic conditioning than the correctly performed full squat.
Mark RippetoeI recommend against a wooden squat rack, for much the same reason that I recommend against a wooden car.
Mark Rippetoe