A worthwhile adventure. I was there a few years ago. Myself and a friend took the private tour, very knowledgable young woman guide, really knew her stuff. Then took the nearby engine factory tour with a retired shop foreman (Heinrich) as guide
Don't remember the cost but relatively cheap and the degree of knowledge by the guides was far better to me than just wandering around on my own. A new E Class had just been announced and the car park had a couple hundred taxis with the drivers attending an Open Day. An enjoyable day, you will love it.