The 03 is a fine rifle - no longer in production - but a fine rifle. I used one on my last hunt in Austria. My .404 is built on a CZ action, and I owned another for while.
I don't hunt with extra magazines with any of my rifles to include my AR feral pig rifle. In the military yes, but hunting? No. I don't do it for dangerous game either, and I know no one who does (not many 98's out there with detachable magazines). I simply top off through the top like any other bolt action. So magazine interchangeability is a non-issue.
What I do really like about the trigger group design of the R8 is that it puts the trigger below the magazine. It's a brilliant concept. The resulting rifle can carry a full length barrel and yet remain very compact. It is one of the advantages often cited, and accurately so, for single shots like the No. 1. That is the genius behind the R8 design.
Though a fine rifle, I have couple of issues with the 03. While barrels are indeed interchangeable, the scope is mounted on the action. The scope of a R8 is mounted on the barrel. Most R8 owners dedicate a scope to each barrel. Thus when I change calibers, no sight-in is required. With a scope on the receiver, the rifle should be re-sighted with every barrel change. Rather inconvenient on an African hunt. I also don't much care for the 03's cocking lever. For those who haven't seen one, it is small flag type left/right lever at the rear of the bolt. Unlike the R8, S2, or Krieghoff intuitive slide cocking mechanism, the flag is somewhat counter-intuitive and requires a very different manual of arms from any other rifle in the gun room. That would seem more of an issue to me following up DG than trying to switch magazines.
Apparently a lot of other people aren't that enamored with the design as well - Mauser ceased its production last year.
https://www.mauser.com/en/mauser-news.html?tx_news_pi1[news]=29&tx_news_pi1[controller]=News&tx_news_pi1[action]=detail&cHash=d02f7c08f362899ae996b278b42a47b0
Perhaps you could go into a little more detail on the "bullshit" design faults of the R8?