The H2S and H2D share the same fundamental hardware: same chamber heating, same max nozzle temp, same speed, same AMS. The H2D adds a true dual-nozzle (IDEX) toolhead for two-material printing (not just multi-color via AMS), LiDAR for first-layer inspection, and support for the higher-power 40W laser. Both machines accept Bambu's optional 10W laser and cutting module, so basic engraving and cutting is not exclusive to the H2D.
If you need soluble supports for PA-CF parts with complex internal geometries, the dual nozzle is genuinely useful. If you want laser engraving or light cutting, both models take the module, only the higher-power 40W upgrade is H2D-only. If you need none of the dual nozzle, LiDAR or 40W laser, you're paying $350 (street) for capability you'll never use.