Ken,
Me and my brother do this when we are working together. We are about the same height. Squatting like you see that man doing is quite natural, and is easier than bending over at the back. It is always better in the long run, after all, to bend at the knees than to bend your back.
As for little room for error, I will say this: Watching the technique, it does look a bit haphazard, and inaccurate. However, I have discovered that it is in fact superbly accurate. We at least always get good straight, clean notches that are exactly the depth we want them. With scoring from above, I always have trouble with some of the scoring marks remaining on the finished timbers, whereas with this technique I have never had a scoring mark too deep. So really, Ken, I am convinced that this is the superior method. But it does have the obvious disadvantage of requiring 2 workers.
Will,
I have had a lot of problems with ash developing large splits along its length, and can see how this could end up being a serious problems. As for ease of hewing, I really ought to see how well ash stands up to me new tools and my latest evolution of technique.
Hickory I like to work with. You have to be patient with it. I find it is always good whenever you can make timbers without an enclosed center. In other words, they will generally be a bit more stable if you split the log down the middle at some point. On a timber currently in progress, we have a hickory log about 18" in diameter, from which we are cutting 2 9x6 posts. What we are doing is first hewing all 4 faces, then splitting it in half very carefully directing the split to keep it within a 2 inch window. This can be done, but it does often require you to go back after you have split it with an axe or saw to cut through areas where you had to direct the split a little bit. Obviously you can't do this with smaller logs, or very long lengths. The posts in question will have a finished length of just under 8 feet, so in that length a reasonable split is certainly manageable. If I were making 40 foot sills or some such, then I wouldn't even consider trying to split it first (I might, though, have a sawyer cut it in half, which was certainly done in the past)
Off topic a bit, I just bought 4 dogs for like $35 including shipping. The sipping on them is almost as much as what I paid for them. Every once in a while ebay does give you something worthwhile
