This is a question whose answer is highly dependent on the hair that is being shaved and the equipment that is being used to shave it! Some people find that a particular brand of the blade will last them for 5 shaves, and some will find that the same blade can last for 20 shaves.
So, why the big difference? Quite simply, the variable factor is the strength of the hair that the blade is being asked to cut, the analogy of human hair being as strong as a steel wire of the same thickness is accurate. Hair strength, or thickness, varies enormously between us blokes, and also where the hair is growing on the body.
If you want to buy beard combs & brushes, then you can search online.
A generalization is that dark hair is normally thicker than fair hair; also, the hair on the legs is generally finer than hair within the beard area. So there we go, dark hair within the beard area is pretty much the toughest hair you can get and this is why shaving blunts the microscopically thin blades.
Razor design – it's a "tech" thing!
Manufacturers very cleverly design their blades with features that help the cutting process and it costs them a lot – Gillette was rumored to have spent over $1 Billion on developing their Mach 3 razor. The original razors were "cut-throat" straight razors that relied on pure sharpness to cut that pesky coarse hair. As technology advanced, the safety razor was developed which protected the skin as the beard was shaved.