The original design has contact points, rollers and guides, that touch the film within the visible image area, not only at the edges. The mechanism contacts the same surface being viewed.
The new design moves all contact points to the edges of the film. No contact with the emulsion or acetate side within the image area. This requires tapered guide surfaces, which are straightforward to produce with CNC machining or direct 3D printing.
The original could not use tapered rails. The guide rails had to remain vertical to release from the injection molding tool. A taper in the wrong direction locks the part in the mold and requires side-actions in the tooling, which weren’t cost-effective for this product at its original price point.
Keeping contact at the edges reduces scratching and pitting of the film in the viewing area over repeated use.