I run a small custom shop here at PHXHolsters.com.  I simply do not have every mold for every gun that is being or has been manufactured. As a result, there are times when I will need your gun and or magazine to use as the mold.  There are advantages and disadvantages for you the buyer and myself: some of the advantages and disadvantages are listed below.
ADVANTAGES
1.  You are going to get a custom and exact copy of your gun because the Kydex is wrapped around your gun and not just a mold.
2.  I have the ability to custom adjust for each and every gun.
3.  If you are local it is an easy drop off and pick up.
DISADVANTAGES:
1.  If you are not local - things get more complicated for us both.
2.  Your holster has to be fabricated from a mold.  (This is how all the big shops do it.)
3.  Communication regarding customizations (lights, RMR, etc) can be misunderstood.
DISCLAIMER:
I do not want to misrepresent using molds. And I have just recently bought and set up a vacuum former to speed up the holster-making process.  If the molds are a good representation of the gun - it will be a great holster!