So the only way this makes sense to me is for someone who travels across time zones as part of a single trip, or maybe doesnt wear their GMT watch when they are at home. Otherwise you end up adjusting both hands anyway.
On my crappy GMT’s, I set the local time to local time and the gmt hand to my most relevant remote time, so currently my watch is set to British Summer Time and Pacific Daylight time. When I fly to the office, I set my gmt hand to BST and the hour hand to PDT. I don’t see how this would be any different if the hour hand jumped not the gmt hand?
Is the intent that I leave the GMT hand actually on GMT and do maths? At that point I might as well have a three hand watch and just do maths.