(I think) you'd get the same reading mate
The controller you've made controls the volts to adjust the flow so (again, i think) the draw from the battery would vary, and so the output would be the same as the input...
So that screen you have put in the controller should show the varying voltage differences without the need for another voltmetre...
(I'm assuming in the pic, your battery is on charge?)
(Spruce or ian sheppard may be able to tell you for definite!)
It looks good mate, you've done a good job
I was going to do one of these myself after your post, but i managed to get a varistream for £25, but definitley one for the future!