Its an interesting concept, that has no practical use for most gun owners... Unless they live in a location that limits the number of "firearms" an individual can own.
I do like the fact that the entire grip is changed, as they can better shape the grip for that size hand and grip length you are using. Sticking an extra thick or thin bit on the backstrap is better than nothing, but not the best solution for adapting to hand size.
Now for the military and police armories... The concept is much more viable.
Especially the military... In addition to the ability to adapt the pistol to the user's hand size...
One simple and very durable part (the sub frame and its integrated slide rails) has the serial number, and is the "gun". Everything else would fall under the category of "spare and replacement parts".
Every other part can be swapped/replaced as needed without ever changing the serial number. You can rebuild a damaged pistol, or repair a malfunctioning trigger group... As long as the sub frame is intact, and undamaged, the serial number is the same. This cuts down on the amount of critical tracking needed.
As it stands now, an unserviceable firearm must go through a disposal process, where it is shipped to a facility in Alabama for destruction, and has to be removed officially from inventory.
