I wanted to visit Tibet, and based on the very positive reviews for this company, I booked with them and was not disappointed.
Our contact was Janet, and she was great both in preparing the trip (including answering immediately to our questions, even when it was midnight in China) and in making sure everything worked out smoothly (including checking at 5:00 am that we indeed got our transport to the airport).
In Tibet, we took the "5 days Lhasa & Yamdrok Lake" tour. On the way to Tibet I had a stopover in Beijing, and took the opportunity to do two days of sightseeing. I asked Janet for recommendations, and she suggested the day tours "Hiking on Jinshanling Great Wall" and "Tiananmen Square, Forbidden City, Summer Palace, The Temple of Heaven".
I think these tours were indeed the highlights of both Beijing and Tibet for us, and if I would go to Tibet again (e.g. with my wife and son, who could not come with us this time) I would book the same tours.
I usually prefer to organise my travels myself, but it seemed the only realistic possibility to get a Tibet travel permit is to book with an approved travel agency. In general, when booking with an agency, you pay slightly more and have fewer options, but on the other hand, it saves a lot of preparation time and is a lot safer if you don't know much about the country you travel to.
In Beijing, the expertise of the travel agency got our group on the Great Wall at a spot where almost no other tourists were - this spot was (almost) inaccessible due to a construction zone. On my own, I certainly would not have discovered this possibility. The other tour let us see the highlights of Beijing in one efficient and cheap bus tour, but on the other hand, it included a bit of (I guess) sponsored stops at a "Traditional Chinese Medicine" institute and a pearl factory. I would rather have paid a bit more and skipped these promotions, but they were short, and I just relaxed with a drink in the air-conditioned cafeteria. (During the preparation, Janet told me about the "shopping" that was included, and the "Jinshanling Great Wall" tour without shopping, but for the "Forbidden City" tour there was no alternative without shopping.)
In Tibet, the first day was for acclimatisation to the thin air, and indeed I was out of breath from just climbing the stairs to our hotel room. But after basically sleeping the first day, I was OK the next days, and for me the visits to the monasteries and the Potala Palace were absolutely amazing. Individual photos cannot convey the atmosphere of these large buildings with thousands of small and large rooms full of statues, pictures, scriptures, every square inch decorated, and everything with ancient traditions, but still in use today. This was the main reason I wanted to visit Tibet, and I was not disappointed. My daughter also enjoyed the mountain tour a lot, although to me it seemed surprisingly similar to the Alps (we live in Switzerland), just 4000 meters higher, and with cows replaced by yaks :-)
The only little inconvenience was the transport from and to the airport, which is about 50km from Lhasa. When we arrived, the driver was not there yet (it turned out his previous clients, who needed to go to the airport, had been late), and after he arrived, we still had to wait for some hour for the next clients to arrive at the airport (their plane was delayed). Well, that is what you get with cheap transport (included in the package). The opposite thing happened on the way back - the transport that would have been included in the package did not go early enough for the plane that was booked for us, so we had to pay 400 Yuan extra for private transport. But then this was super efficient, picking us up exactly at the promised time and bringing us to the airport at the right time to check in.
Summary: Amazing destination, very well organised tours, would book again with them!