If you're attaching the Capture to the TT Pro Speed Belt, the only issue I can see is trying to attach it. The screw is barely long enough so you'll have to force it. You may have to purchase the long screw if you want that extra length. The PROpad comes with the longer screw.
If you don't use a grip, its up to you if you want the PROpad. Some who don't use a grip still purchase the PROpad because it provides extra padding between you and that camera. Also, the PROpad allows you to put the Capture horizontally. So when you're clipping your camera to the Capture, you just slide it from top down. If you just have the Capture in a vertical position, you slide the camera from right to left. See my images:




I personally like the horizontal position myself. Less digging and easier to remove and clip the camera in. The camera is a smidge lower if horizontal because it sits a little lower than in the vertical position.
Here is a picture of the TT Pro Belt with the PROpad and CapturePRO
This image is with the long screw on a thick padding. Image is of my ThinkTank Shapeshifter backpack but the Pro Belt is about the same thickness. As you can see, how much the screw sticks out. The long clamping bolts are $10 if you just want the long screws and no PROpad - https://peakdesignltd.com/store/clamping-bolts-long
I see you are attaching it at your hip. In the youtube videos, the owner recommends that you place the clip closer to the front near your crotch. have your tried that position? I mean, yes, it looks a little awkward if you have a long white lens, but I wonder if its more comfortable...


