A pistol is a good exercise. I love it. But I wouldn't place too much effort in maxing out.
A pistol is but one way of unilateral squatting. And the pistol is the most demanding because you need flexibility/mobility as well as coordination/balance.
Of course a weighted pistol is hard. But that is not the point. It's essentially the Bench Press vs Bosu Ball Press discussion. Why would you test your max with an exercise which causes you to wobble and cheat your way up?
Besides, by doing only one or two repetitions, you don't really reap the benefits of the pistol (balancing/mobility) as it is apparent in the video -by which I don't want to discredit the accomplishment.
In my opinion, do pistols for reps.
As for being a "safer exercise" (then the squat) by making the guy more injury resistent, I'd like to see some data beforehand. Mindlessly paraphrasing some coach's latest hype can be deceiving. A one legged squat is certainly tougher on the knees. The load is higher while more stabilization has to be maintained.