I grooved all four of my tires. I have nothing to compare it to - I didn't see the point of struggling for a winter and then adding the grooves to see how much better it would be.
The grooving itself went OK. It was near freezing and a bit windy. I can imagine it being quite a bit easier on a warm summer day, but it wasn't too bad. I did it in a total of three sessions. The first was a trial run - I did maybe a half dozen front lugs. Then I did most of the rest; I was getting physically worn out pushing that tool... Finished up with 26 rear lugs a couple days later.
Only used it three times in snow so far, but no problems whatsoever with traction. Thought I'd share a few pics that (I think) demonstrate why it works.
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