I guess because it's technically a replacement part. I don't think a *thumb rest [generic]* would make someone that much faster. I have a 22/45 .22 that is basically an open gun but a .22 it has a *thumb rest [generic]* on it. The advantage in that case is it allows me to index the gun alot better. I thought about trying one on my CZ but with bladetech holster and my hanger that would be alot of changes for something that I don't really need