Whilst I agree with practically all your points Ken there is a clarification to be made. If one is crossing from the Tormek to say a 1x30 leather belt in order to hone and say you want to increase the angle by half a degree as is common for some steels, you would want to be as precise as possible and be confident of your angles. A goniometer isn't always easy to read precisely and the sharpie method on a flexible leather belt won't tell enough.
But yes, my advice is stick with one (preferably the ks 123) and don't mix and match.
But yes, my advice is stick with one (preferably the ks 123) and don't mix and match.