How to duplicate/extract out a model from the one you are currently modeling and you can switch either one to edit? Any hot key! Not subtool~ 
For example, if you want to demonstrate two brushes’ property, you duplicate your model and create another next to your original model, so you can easily see the different effects of each brush.
You can clone your sub tool from the tool menu to the right or at the top of ther UI. Then click append button in your currect subtool pallet. You can now move the cloned version to the side.
I watched a tutorial the instructor just “drag” then you have two identical models on the same plane. Just want to to know how to do that~ 
I figure it out, it’s snap shot function! But still not to know how to switch back and forth.
Yeah, would like to know that too!
Didn’t even know you could switch from one to the other. Would be awesome to have two “active” objects on the canvas at the same time. Great when comparing different tools.