Most of my experience with flat filing bases has been mentioned in these many posts. But, It's an open forum, I I firmly believe that everyone is entitled to MY opinion! ;-)
1st, I will remain emphatic on the position that removing P-Tex from a base high ski with a metal file is an exercise in futility. (Those Montana machines make it look like the best time for money swap I have ever seen)
2nd, It is ridiculously easy to add base bevel while trying to remove it. In fact, unless the file is backed with a 2inch I beam (figurative), it's hard to even get near to flat. A straight edge confirms this, no need for fancy angle measuring gizmos. (Of which I have many due to my metal work and machining interests)
3rd, cabinet scrapers dull rapidly when rubbed on work hardened ski edges.
I use a high speed steel (HSS) tool bit with a sharp square edge, and still the edges on the ski defeats the sharpness of the tool (Scissors, paper, rock)
4th, ski edge files are pretty pricey and don't last long on some ski edges (too hard), making the shop prices seem more reasonable.
5th I still "flat file at least a couple times every year, and then take the skis in for a pass through the Montana to bring out the flatness.
6th The fancy machines will NOT flatten the bases and the edges. The stones that grind P-tex do not want to see steel, and the "ceramic stones" that do the edges can not be set to "Zero" . Or if they are, don't cut metal.
Damn this flat base thing is hard!
Still, My choice is to begin with "zero-zero" base and side, and let the rocks do their thing! ;-)