Yep you screw it right into the bottle, and its quite a long screw too. The cleaning of the bottle is probably going to get annoying very much very soon.

I've decided to keep the stem and the bottle anyway but it was a close call as all in all this product does have quite a few downsides to it.

My stem came without the screw in barrel adjuster cable stop and I don't know where to source one (in Germany), so thats a bit of a let down.
Also since I don't use a riser kit on my PD J5 bracket I've had to move my extensions quite a bit apart because otherwise the bottle wouldn't fit between the extensions. Before that I had my extensions a bit closer together so that my hands would touch. I'm not qualified to judge if that change in fit does impact aerodynamics in any significant way.

On a minor note I'm not exactly fond of the bottle being black (but I knew that beforehand and I'm not blaming PD for this design choice).