Nice work! The things you learned about blade angle are universal across all razors. The level of effort and cool factor versus real world results are something only you can judge. In full disclosure, I've never used an old SE razor, but they have a reputation for being a bit toothy. I applaud how well you've done on such an unforgiving blade type, all done very early in your conversion to traditional shaves! Kudos!
Slight irritation
does not have to be a part of your shaves. How can you possibly judge tiny differences, while clearly defining the areas that need work, all without guessing?
Alum. It's the gold standard. It separates the perfectly acceptable from the acceptably perfected. It never lies.
Some here use it literally as positive reinforcement of technique through cool refreshing sensation. If you truly shave well, the alum will feel soothing, as if you're moving a cold, smooth stone over your face. It could also be called positive punishment when the technique slips.

If you stop in to a local pharmacy, look in the antiperspirant/deodorant shelves. You will likely see a product that is a crystal block or stick for use under the arms. If the specific ingredient listed on the packaging is Potassium Alum, and this ingredient alone, it is one and the same as barber's alum. This product provides one of the only truly objective methods, albeit in an indidual way, of affirming perfect technique.
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