I got 3D Data Plot from the App store. My first shock was that there are no menu bar items other than About, Hide and Quit. No File, Open, Preferences, Save, Updates, or Help. The app comes pre-installed with three sample data sets. These show promise in that they can be manipulated in ways that one would expect. The big problem is that there seems to be no way to import data from a file. The App Store video shows a window magically popping up to fetch data, but after viewing it a dozen times, I still do not see how to get this window to appear. The App Store description says to "tap 'share button'", but no such button exists in the iMac app.
Under settings, I noticed that the free app only allows ten data points. For an in-app purchase of $7.99 you can enable more points (actual number not specified). I decided that the file reading might be opened up if the purchase was made, but the app does not behave any differently after I threw away $7.99 plus tax.
The program has created a folder on my iCloud Drive called 3dDataPlot. It holds an empty file called sample.txt. I do not have privilages over this folder, and cannot copy a data file into it.
Clicking "App Support" in the App Store brings up a webpage that is not in English, with the heading
雁来十番地 / Kariki No.10
I don't think that this webpage has anything to do with the author, Yukiko Iwai.
I suggest extreme caution when considering this app.