You really need to look at your usage to work out if this is worthwhile given your own circumstances. It might not be as good as it seems at first sight. Many people make calls to many other mobiles - if you are calling to non-E-Plus customers then the rates are quite high, as would be roaming costs when abroad. As has been already noted, E-PLus coverage is not good outside of major cities and autobahns...
Even the some pre-paid (pay-as-you-go) deals might work out cheaper. No monthly cost and 14cents a minute for calls to all networks (see
here for an example on T-mobile which has good coverage) works out at almost 3 hours of calls before you exceed the €25 that Base would cost you, also bearing in mind that a months vacation out of Germany just wasted your €25 as you can't take advantage of the inclusive calls...
YL6