Ian, I don’t believe your personal views on this will result in a great schism of the reloading world. To each his own.
The expander you show will get the job done.
I’ve never seen a “M” die expander harm the case mouth unless it was grossly misadjusted. And the benefits that Snakeoil listed are in the positive column. Particularly the creation of that “socket” feature on the case mouth.
Now, with that out of the way, I will say that on a bottleneck casing the depth that the expander spud enters the casing is a lot less critical than on a straight wall casing. So, if you’re dealing with a bottle neck case and you don’t care if the entire neck is expanded to a desired diameter, the distance between the tip of the expander and the beginning of that flare isn’t as critical. This may be where some of the dissension rests.