I've found the depth of these boots to be really good as with over reach boots of other brands I've often found that they are just not big enough to cover the back of the hoof properly. The leather-like outer fabric feels really strong and protective. The double velcro straps means that they are very secure, and I have never lost either of my pairs during riding, lunging or hacking out.
I also loveeeeeee the fact that these are the first over reach boots that I've ever seen to have the colour of the lambskin and outer fabric co-ordinated! I've bought mine from Fur Feather Meds and had them delivered to Finland :) I can highly recommend the over reach boots as well the company!