My husband and I had a fabulous experience with Flash Safaris. In the midst of a round-the-world trip we impulsively decided to stop in Tanzania. Unsure if we could organize a safari in our time frame, I emailed Magda at Flash and she responded promptly. She worked quickly to organize a guide, itinerary and accommodations that suited our request.
When we began the safari, we didn't quite know what to expect, but the entire experience greatly exceeded our expectations. Our guide, Tumaini, was awesome - so sweet and very knowledgeable about everything we saw.
We toured Arusha National Park, Lake Manyara, Ngorogoro Crater and the Serengeti. We also did a tour of two Maasai villages - the modern Maasai outside of Arusha and then the traditional Maasai near Ngorogoro. Highly recommend the former as it felt extremely authentic. We learned a lot and got to do so in a genuine, relaxed manner. The visit to the traditional Maasai village is something I would have skipped. It was very touristy; they tried to force-sell me bracelets that I did not want to buy, and overall the experience left a bad taste in my mouth.
Definitely don't hesitate to go with Flash if you're on the fence. We'd repeat our trip with them in a heart beat!