Custom golf clubs are anything from a single club to a full set of woods,
Mizuno MX-200 Irons irons and putter which have been custom specified and assembled just for you. They may work for somebody else and other people will probably love your custom built golf clubs, but they are yours.
To make an analogy that most of you will be familiar with we will compare
Mizuno MP-53 Irons buying a new set of golf clubs to buying a new suit or dress, there are three ways you can go about this;
Option 1 - You go to a clothes shop and browse around until you see something fashionable and then buy it and hope it fits
Mizuno MX-300 Irons you OK and is comfortable. That is the normal way most people buy their golf clubs.
Option 2 - You can go to the same shops and try a few different designs, maybe even mix and match top and bottom of the outfit, and eventually you will get something that fits OK but you may need to have altered, within the leeway the existing clothing gives on sizes and lengths and quite a lot of people will get a reasonable fit.
Mizuno MP-58 Irons This is very similar to custom fitting your new golf clubs, you are still limited to the small number of shafts and flexes that that manufacturer provides and most will only extend or reduce by 1/2" and at the most 2 degrees loft and lie. The shaft flexes will only be those stamped on the side of the shaft and are different for every shaft manufacturer, very rarely are these actually measured and you better match one of the five or six flexes available.
Mizuno MX-1000 Irons For a lot of people that just isn't enough, and this can still take many weeks.