I have used just and only precision square and never noted any issues by damaging freshly-sharpened edges. Higher risk I have seen in the deburring. It has happened several times that I have failed in the deburring and therefore have been forced to make few extra passes. H.D.I gauge...or its dial gauge tip harms more easily edges.
I'm not an engineer, and tend to use cheap tools. I once went into dollar stores, found a cheap plastic square that was too big to fit against the side of a skate, probably part of a drawing set (or maybe the square corner was on the inside of something), and cut it down to size. I had to search a lot because most plastic squares are rounded at the corner. I verified the angle was right by testing the blade on both sides. But the resulting tool was very small, and I lost it.
Nonetheless it was very light, and unlikely to damage the edge. I may do it again some day.
Plastics typically have a larger coefficient of thermal expansion than metals. Perhaps that means shapes change more with temperature?
With Pro-Filer, I now take a few strokes in one direction, reverse the skate or Pro-Filer, and take a few more and repeat. That evens things out, and there is no uneven edge problem. Also, it is a short enough tool to follow minor blade warps, so they are no problem. Of course, if the gap between the blade and the tool was significant, there would be too much position shift, and I wouldn't get good sharp edges - one of the reasons (aside from reducing scratches) for first putting tape on both sides of narrow blades, to make the gap snug. It also would create sharp edges if the tool had an off-center gap, or if a blade had an abrupt bend, like I am told hockey players sometimes get when blades collide at high speed.
I could do the same even better with the old (about 1930-1950) Berghman sharpeners, if I decide to switch to .5" ROH. The adjustable gap size (I do have one old-style Pro-Filer with a slightly adjustable gap too), and the ease of seeing what you are doing are huge improvements, as long as you use a better quality modern cylindrical stone than crumbly coarse ones that they came with.
It is true that some very good, experienced skate techs manage to produce very good edges without using measuring tools most of the time. I think they just get a feel for what they are doing after a long period of practice. But a lot of the people who use no measuring tools are just trying to work in a hurry, or don't know how to do better.
But I now believe the "magic of measurement" is very useful for less experienced learners who want to learn to do the best they can. It took me a long time to figure out that measurement makes sense for learners. I had minimal instructions (a few minutes or less from the guy who sold me my Pro-filer, a display model that had no written instructions), had to mostly teach myself how to sharpen, and made a lot of early mistakes. E.g., I used to slow down my strokes too much at the ends. The result was that I gradually flattened the rocker on a pair of MK Dance blades, and I didn't even know about the sweet spot (rocker radius transition point). By that time I had learned to take off extremely little metal per sharpening, which meant that the blades lasted me for many, many years and many thousands of hours on the ice - so that systematic change I created with each sharpening had lots of time to build up. In the end, I took the blades to an expert skate tech who could reshape the rocker profile back to the original shape rapidly with a powered sharpening tool.
I also used another expert skate tech when I did my experiment trying to reshape the rocker profile of Jackson Matrix Dance blades to that of MK Dance, using a bench grinder, which created no ROH and probably uneven edges. If I had tried to create the rocker or ROH using a Pro-Filer, it would likely have worn out the diamond dust stone.
I don't think we should be bothered by sometimes going to the real experts who have the real professional grade tools. If we can do most of our own sharpenings, and produce sharper edges (if that is what we want, and I often do, especially if I am to skate on rough ice) and less rocker change (or only the desired changes) than most pros, that is still an achievement.
But I can see how those of you who have invested in purpose-built powered sharpening machines, which don't come cheap, would want to be able to do everything yourself.
This is going to be a very strange idea, but are there metal-cutting router bits that can grind the profile or impose an initial ROH (prior to refinements with better tools) on the relatively hard (Rockwell C of about 60) metal in high end skate blades? I don't have a router (though I might be able to buy one used, or use a router-adaptor that is powered by a hand-held drill) and would have to make a custom (very narrow) router table, but I wonder if that could be done. I picture guiding the router along a desired profile shape with a drafting spline, bent to the desired profile shape, which would first be fit to a printed shape made using software and a printer.
Or would any router bit be completely worn out on such hard metal?