Yes you are right one thing it does not point out is.
Bricks alter in depth and length,bricks with a bed have to work to 75mm, two course 150mm,3= 225mm if a bricklayer has a brick that is 63mm he will make the bed 13 mm to make it up to 75mm.
The head hights for all window and doors work to this gauge, so the brickies mate give a perfect 10mm bed, so usuing a brick that is 63mm deep with a 10mm bed you would be out of gauge by 2mm per brick.
So its 28 course to door lintel 28x2 is 56mm you would be out of gauge,seeing that 3 brick equal to one block on the inner leaf, how would the ties work,wall ties can tilt from the inner leaf to the outer leaf too much of a tilt and the site agent would have kittens and ask you to take it down.
One hospital job i worked on was murder, the bricks were very hard and had been baked, the depth on them were 62mm we had to do joint 13mm deep, the Architect and Foreman came and were screaming blue murder,he checked our gauge and it was 75,150,225,300,375,450,600,
We were correct you do not make 10mm beds because it looks good, you stick to gauge which is what you have to do.
Yes its ok for the lay man, but to say a bricklayer would use it is a load of old tosh no bricklayer worth his salt would do 10mm beds, 10 mm bed would only work with bricks that would be 65mm deep, i have used brick that are 68 deep i then had to make the beds 7mm deep, again with brickies mate i would be 3mm + out of gauge, after 28 courses i would be 84mm + out of gauge.
Work it out for your self,the same applies to linear brick work,225,450,750,900,if i have bricks that are 212 i make a 13mm perp to get back to linear gauge 212+13= 225 again it says the perfect 10mm perp on the bricks, by using the perfect perp you are - 3mm short on 225mm which is what it should me, so after 30 bricks you would be out 60mm.
You can have bricks in aload that change from + to - to 215, so using brickies mate how would you keep the perps running in a straight line.
No i do think its a great tool for the person who want to do a garden wall,buy to say a real bricklayer went faster using this is too much to take, unless he was not a real bricklayer and this did make him faster, go out nect time and see how bricks sizes alter in depth and length, do nor take my word for it, then sit down and work it out.