Optics ready plates for Glock MOS gen.6 models [G19, G17 & other]

The 6th generation of Glock MOS came with unique mounting solution, that does not require an adapter plate for many of the existing red dot footprints.

In what situation do you need to buy an adapter plate for Glock MOS gen.6? 

Primarily in case that you want to install a red dot with unusual footprint - such as Aimpoint Acro, Holosun 509T, or many others. 

Another reason to get aftermarket adapter is to get better quality adapters for your gun.