UN I suspect is being driven by numbers folk with the decision to have a date. Yes, more folks like a date, but the purity and sanctity of the enamel dial is ruined by it.
The UN Cal 320 is un-necessary, what on earth are the designers thinking...does anyone care about the caliber designation? Preferable, if absolutely needed, to be on the caseback, where it doesn't also ruin the purity of the classic elongated romans which I happen to love and own several pieces with them...Donze enamel dials are simply lovely, why go ruin it with superfluous additions.
Here are my executions of the elongated romans Donze enamel dials, One with sub seconds and the other with central, plus the 150th Anniversary piece for good measure! :