I have done the tour two or three times over the past years. I can recommend it as it's a nice bus tour taking a route starting from T2 airside driving down the tarmac past T1, LH maintenance, fuel depot and further on to threshold of runway 18 and backwards.

Tour start to enter the bus is opposite T1 at Meeting Point "Airport Experience Tours" located on the connector bridge between Terminal 1 and Frankfurt Airport Center (FAC)/ICE train station and bus takes you to an outdoor security screening first before it moves airside. You can take your camera with you all the time to take plenty of photos (through the windows of the bus though). There's a narrator onboard explaining interesting planes, types and their destinations and will give some interesting info on airport statistics and operations (in German only if I recall correctly).