I corrected your link, elcammeno, as it wasn't working.
The custom fit has been around a while. The theory of it is fine but is incredibly expensive and wouldn't actually seem to have possess long term benefits over and above any other prosthesis. From discussions amongst surgeons I was party to when it was first brought out, the overall benefits seem minimal, not justifying the additional cost.
So far as other prostheses are concerned, they have quite a range of sizes fo both component with only millimetres of difference between the sizes. For instance, there are ExEx large, EX large, large, medium, small, ex small and exx small in most makes, with tibial inserts from 5 to 15 milimetres in thickness in 1 mm steps to make up for bone loss which almost always occurs in the tibia. The general view is that this makes an assembly that is pretty much "custom fit" anyway.
However, you pays your money and you makes your choice. If you like the idea, then by all means go for it.