This topic came up when the PDGA Technical standards were updated.
https://www.dgcoursereview.com/forums/showthread.php?p=3356822#post3356822
It was suggested the reference to MDGF is an FYI rather than the PDGA granting them any authority. I think we should use the PDGA standards for mini sizes instead of confusing people with some other organization that uses English units when everything else in disc golf is Metric.
MDGF = #NotMyMiniDiscOrganization
Just because Mini Disc Golf is a fringe of a fringe sport doesn't mean it's a free-for-all. Also, I think blurring the lines does a disservice to what each class could be.
Disc Golf is fun. Junior Disc golf is fun. Mini Disc Golf is fun. They also feel different from each other. That's why there are 3 classes of Basket Size, and 3 classes of Disc Size.
Manufacturers also have drawn this distinction. They are going to make the 5.9" (15cm) stuff so they can sell lots of them as "PDGA LEGAL MINI" but they also are for a different purpose than mini disc golf play. They are also simultaneously marketing them for Junior Disc Golf.
Have you ever tried to put a 6" Junior disc in a Mini basket? It barely even fits in there, let alone being able to catch them well.
From MVP:
The Macro Tesla is an 80g and 15cm diameter version of the famed MVP Tesla driver, designed for Macro Disc Golf with the upcoming Black Hole® Macro Basket. Macro discs conform to the PDGA maximum diameter for mini markers, but are much easier to grip and throw naturally than mini discs. The Macro Tesla has plenty of stability to handle a full-bore rip, and has been tested at extraordinary distances by our design team.
The Black Hole® Macro is designed to be the best Macro Disc Golf basket on the market. The 39-inch basket is designed in the Black Hole® style but built for our 15 cm Macro discs.
From Dynamic:
The Dynamic Discs Junior line of discs are a scaled down version of their full-size counterparts, and they are designed to fly with similar flight characteristics. With surprising stability and glide, the Junior line of discs are a ton of fun to throw. We've designed the Junior Recruit basket specifically to catch them well. When paired with the Junior Recruit basket, Junior discs are great for setting up a small, fun course around your house, yard, or office, or even to introduce younger children to the sport of disc golf.
The Junior Recruit is designed to exactly mimic its bigger counterpart in the ever popular Recruit basket. ... Coming in at just under 3' tall and 18" wide, the Junior Recruit is a perfect fit for an office, a playroom, or even a classroom all while pairing perfectly with our newly released line of Junior discs!