Disclaimer: my opinion only - but based on experience.
uDisc used to be the 'go-to' live scoring app for tournaments. Pretty cool, easy to use, only one player had to have uDisc...the other players could be added even if they didn't have the app. But then PDGA came out with their own live scoring app and that has become the 'go-to' for some tournaments. For example: The Memorial used PDGA's live scoring as the official one and uDisc as the back-up.
uDisc's app provides a lot of 'extras' that PDGA's app doesn't. It costs money to develop and maintain the app and its features. uDisc, like other apps, has a free and paid version. The paid version comes with your PDGA membership, but if you aren't a PDGA member, you have to pay for the pro version. I wonder how many people really do that....especially since most disc golfers just need it to find courses, find their way around the course, and keep score - the free version does that.
When we pay for the pro version, we are paying for the "bells and whistles"....just like buying anything else....a car, a house, whatever...the fancier it is, the more you pay.
Is it worth the $15ish for me? Not really, but I don't have to be concerned with that as I get it via my PDGA membership. PDGA most likely has a contract with uDisc for members getting uDisc Pro as part of the membership. Will it last? Hard to say. The price agreement may go up a bit and PDGA may add it to the membership cost or may consider it minor enough to not change anything. Or PDGA and uDisc may go their separate ways since PDGA has its own scoring app.
Bottom line, IMO, it's not a big deal....each person just needs to decide what they use uDisc for and if the Pro options are needed. If the Pro options are needed, then the question becomes...is the price worth it?