Anibal Salinas of @Weapons_armament_research did this custom Glock grip modification so he can see how much ammo is left in the gun. He uses an ETS Glock magazine which has transparent mag bodies. He cut a hole into the grip and epoxied clear windows into the grip. He says it is as strong as the factory grip as far as he can tell. Live fire testing still needs to be done but it looks great.
You might be asking if the window compromises the grip’s strength and durability. Salinas said, “I can squeeze the grip (without magazine) with all my strength and I cannot flex it anymore than I could stock.”
Seeing into the gun and knowing how much ammo is in it can be a huge benefit. It is like the fuel gauge in your car. It’s a feature that makes your life easier because you just have to look at it to see how much gas you have left instead of mentally keeping track of your mileage or pulling over to look in your gas tank to see how much fuel you have.
This custom Glock grip modification prevents a similar issue that gun users have to deal with. Often, shooters count their shots. In some instances, the shooters have an idea their mag is low and swap out their mag for a fresh one. With this transparent window, coupled with the ETS transparent magazines, you know exactly how many rounds you have left in your gun. How cool is that?