OK. That's an interesting gadget
I would by a potato ricer before I bought that thing
My take on it?
You don't need "adjustable bristles" for different coat lengths. The thing is only going to go down as far as it takes to reach the skin (more on this later). So what if you have an "extra" 3/8" of bristle exposed?
This thing will never reach the skin anyway unless you have a short coated dog. These types of brushes are pretty much useless if you have a Collie (like shown in the beginning) or any other dog with hair over an inch in length. You need a tool called a "rake". And they come in all sizes and shapes, but they work and are strong enough to get the undercoat out of a coated dog. It's mostly the undercoat that you find everywhere and a bristle brush won't touch that.
If you do
have a brush that looks similar to this, without the protectors on the bristles for the idiots who would use a wire brush on an English Bulldog, and you get dog hair stuck in it, use a comb to comb it out. Trust me, you'll need two hands with that gadget anyway to pull the hair away from it, just comb through it, like I've shown below. And those are various rakes and strippers on the table.
Save your money and get the bath gadget thingy made by hydrosurge. That looks doable and will loosen up more pet hair than that brush would