That simple mirror arm was not fitted to Kats.
All original Kat mirrors have arms with pivoting 'elbows':
This allows the mirror itself to be horizontal while mounted on Kat clip-on 'bars, which gives you the best possible view, width-wise, of what's behind you, and it gets the mirror out a bit wider.
Those mirrors you posted will work ok, but I doubt you'll ever get them horizontal, and you'll likely get a great view of your shoulder and not much else...
If your OCD doesn't play up, like mine does, then go for it.
As an aside, DR650 mirrors have the correct elbow, and AFAIK are still plentiful and available.