I prefer not to do IP redirection. It seems to me like an unnecessary complication and full of pitfalls. But I also know many companies continue to like the idea. So I seem to be in the minority ;(
Here's one pitfall: regular googlebot crawls come from the US - so it won't get redirected to see other versions. Also, unless executed flawlessly, IP redirection can really frustrate users who are traveling, or expats, or researching for another country, or using a German ISP from a UK hotel, etc, etc.
If you do redirect, then at least make sure there is a regular click path to the other country versions for search engines to crawl. And definitely make sure that each country version of a page has its own unique URL.