What I personally wouldn’t do is try to do the math to figure out the break-even. Maybe if money was the #1 reason why I wanted a Sparx, but honestly that was so far down the list of reasons that it was kind of irrelevant.
I also feel like my time is worth something, not to mention the time wasted skating on a bad sharpening.
The convenience is worth far more than any kind of perceived or real monetary savings, to me at least.