The H2S and H2D share the same fundamental hardware: same chamber heating, same max nozzle temp, same speed, same AMS. The H2D adds two specific things: a dual-nozzle toolhead for true two-material printing (not just multi-color via AMS), and an integrated laser for cutting and engraving.
If you need soluble supports, for PA-CF parts with complex internal geometries, for example: the dual nozzle is genuinely useful. If you want a laser cutter, the H2D saves you buying a separate machine. If you need neither, you're paying $650 for features you'll never use.