I have three shoe trees that I am using in different dress shoes that I own and these work extremely well.  The main shaft is spring-loaded and the form of the front of the shoe tree fits into my different shoes very well.  One of my pairs is a Donald J. Pliner shoe that is one piece of thin material from front to the heel and as such is very subject to warping without some kind of support.  The Woodlore shoe tree works extremely well.  This was my first time using shoe trees and based on this experience, I will be purchasing them for all of my shoes.  I have not yet tried them in a more men's dress boot kind of shoe - all of my shoes are non-laced men's dress shoes.  I normally wear a 38-40 (European size) and the small size shoe tree fits very well with this shoe size.