[KensRedZed]

Your reasoning is spot on, Andy. 

We use all three systems in the clubs where I race.

1) Hudy for tires on aluminum wheels
2) Razor for tires on plastic wheels mounted on axles
3) Proses style truer for profiling the edges of the tires between races/heats.

Originally everyone in the club said "Get a Hudy, and you're all set". Not entirely true. You get what you need or you aren't competitive.

If I were to just race at home with my neighbours. I might skip the truer altogether and go with slip on silicones. Clubs have rules that need to be followed.