I am going to Germany in april of next year. I am a huge history buff and found a city tour company called Insider Tours? I want to know has anyone had any experince with them?

I used them in Frankfurt and was pleased with the guide and the tour.

Yes, I used them last fall for their original walk which was an overview of Berlin and the day trip to Sachsenhausen concentration camp. Both were excellently guided and I learned so much on both. I wouldn't hesitate recommending them or doing other tours with them. Lots of specifics in my Berlin trip report here on fodors, click on my name above to access it.

We took 4 of them in Berlin this summer. The Cold War and Jewish Berlin were wonderful. The overview tour was very good too. If you want to go to Potsdam I would recommend going by yourself.

I have been on 4 of their tours in Berlin, and have been very happy with them. For 12 euro, for a 4 hour tour, you can't beat the price, and the quality of the tours guides is exceptional.

As an FYI - The Frankfurt tour company, Frankfurt on Foot, which was once listed as an Insider tour, is just a stand alone company since several years. Don't want anyone to get frustrated in case they go looking for a Frankfurt tour from the Insider Tours website.
www.frankfurtonfoot.com