He says "It works well, but it comes at the expense of power, and heat. HSS works the flash really hard."
That makes it sound like the flash is getting the job done, but is paying its dues to do it. One reality is that HSS does absolutely nothing positive to increase the ratio of flash exposure to ambient exposure, as you increase the shutter speed, but a leaf shutter can keep increasing that ratio long after the SS point where the ratio
drops due to HSS with a dual-curtain shutter. A halving of guide number for each doubling of shutter speed means a flat-line for the
ratio, because ambient light exposure decreases at the same rate.
The ratio is the same for the two shutter types at slow shutter speeds, then as you increase shutter speed, at some point the dual-curtain design drops the ratio and then flat-lines at that lower-than-peak level, equivalent to about a stop slower than the maximum sync speed (less than max). The leaf shutter still climbs in ratio for at least 2 or 3 more doublings of shutter speed after the dual-curtain ratio drops to its low-ratio flat-line. The leaf shutter can gain 2 or 3 or more stops of flash:ambient ratio before you reach its SS limits (or diminishing flash returns).
Now, if you are really bothered about beginners (and not, as I suspect, just beating a drum) then you'll realise that a beginner won't know what Guide Number means (whether abbreviated or not) but can easily understand the message "... at the expense of power".
A relative waste of power. Most of that light that makes it to the sensor plane is hitting the shutter curtains. Beginners need to get realistic models in their heads in the beginning. They need to know that dual-curtain shutters are a gimmick, although a useful gimmick in some ways like getting shorter pixel exposure times, but
NOT in helping with flash:ambient exposure levels, or being able to freeze vertical camera/subject registrations during the full sensor exposure interval.
All that HSS can do is provide a fast-strobing auxiliary lamp (which, hopefully, looks like a continuous lamp in most intended uses) that is housed in a flash, and communicates with the camera in flash protocol, and is only "on" when at least one row of pixels is available for exposure. It has no other "flash" qualities which are present in the range of shutter speeds where normal sync works, where the flash exposure is shorter than the ambient, and where increasing shutter speed increases the flash:ambient exposure ratio.
Whether you are using HSS with 1/320 or 1/8000, it emits light for the same period of time, about 1/160 - 1/230 or so. The slit, which moves over the sensor at the same speed in both cases, is just much narrower at 1/8000, and prone to more inaccuracy in consistent exposure, especially with pulsating light like HSS flash. 1/8000 on a DSLR is only 1/8000 in terms of how long each row of sensor pixels is exposed. The full time interval of any sensor exposure is actually as long as about 1/160 or a little shorter, in reality. A bit of an high shutter speed "farce" if there is any fast vertical motion in the scene or fast vertical change of registration during that relatively long exposure, with both HSS and ambient exposure, but not with normal sync flash, possible at higher shutter speeds with a leaf shutter.
