I have a write up about all the differences here...
http://www.ocean-explorers.co.uk/index.php?option=com_content&task=view&id=16&Itemi d=30
for the extra couple of quid it really is worth it to get the better valves...
FYI interest I have DIRzone, Scubatec and Halcyon valves, and the H ones need servicing least often.