Just a guess on my part but tech training and the attention to detail/time required is likely the reason for SP to give up which in my opinion is directly related to the industry standard outdated business model. There is also some rumor about the C series being dropped, my opinion it would be for the same reason. The standard “common” in-line barrel type regulator like the s 600/620 and G series are common across all brands in basic style/construction, it takes very little time to cross train for most brands, the D series can be intimidating the TFX may meet the same issue but since Before Atomic there was no “Best” they may do better.