The product is 120x105x210 in dimensions. Cavity almost as large as exterior. You will need at least a width of 50 mm to feel something because it the minimum width between plastics pistons and no way to tighten. If you are not this width, leave it, you wont feel anything other than the entrance.
I feel really frustrated to can't review this product because of this but it's better than no other fall for it. maybe later a smaller version