Right, I did a minute of stretching then got on with it. I like doing any sort of exercise slowly, so I decided that if I got to the end and was still in the middle of a rep, I'd complete it.
Results: 2m, 2.4 secs. 13 full squats.
I went for 50kg, and to avoid any possible whinging from the purists on here about my machine, for arguments sake let's say that's only equal to 25kg normal. (Next time I pass a gym I'm going in as a guest to do a few squats the normal way and see exactly what sort of ratio exists.)
I definitely felt a pinch from it, but I wouldn't say it's all that taxing. I reckon my legs will be fully back to normal in a few minutes, so I'm going to try again on 60kg sometime in the next hour. I'll report back soon after.
/Oh yeah, I went up 'explosively' to begin with as the article mentioned, but that made my knees click a bit (think I was straightening my legs too much) so I calmed it down after the first three reps.