The Chelsea, Chukka boot tree looks very good aesthetically but not practical in usage. Many people have reported it ruins the elastic very quickly, difficult to explain but just imagine shoving that lump of a heal into the boot.
I don't agree with that assessment. The boot tree does not apply any pressure to the elastics when in the boot. See my new Havana pair below, note the elastics are completely flat, the tree does not contact them at all. The widest part of the tree is the bottom of the heel, which is no wider than your actual foot and only passes the elastics for a second while you insert, which the elastics are specifically designed to accomodate otherwise putting your foot in the boot would ruin them. Your natural movements when wearing the boot apply waaaaay more stress to the elastics than these or any other shoe/boot tree, as with each step the movement of your leg forwards and backwards stretches the elastic. This is why you see really old RM pairs with elastics that are dramatically stretched yet have never had trees inside.
The only difference practically between the boot trees and a traditional shoe tree is a small amount of rear ankle support to lessen creasing of the rear portion in the same way as a shoe tree would to any other part of the boot. But this is a pretty minor benefit, if you already owned shoe trees I wouldn't recommend buying new boot trees just for that. I definitely am not concerned about damage to the elastics.