OK, you'll have to explain. I'm not getting why this is necessary. A knife works great for me.
If a mango is ripe, I simply score the skin in quarters - once all the way around, and then a second time at 90 degrees so the skin is in 4 equal parts. Then I peel the skin right off, which is easy to do if the mango is fully ripe. I then eat it whole, leaving 1 piece of skin still on the mango for a solid grip. I don't like to leave any waste on the seed so scrape the seed off with my teeth.
For serving, simply cutting the mango close to where the seed should be, and then scoring as shown in the video and running a knife along the base of the skin works really well for chunks.
For a green unripe mango, using a peeler, and then a knife to cut close to the seed, works just fine.
It seems to me that these gadgets leave more waste than cutting directly against the seed based on the individual mango you're holding, and don't account at all for different shapes and sizes of seeds. And then certainly leave more waste than scraping with teeth!
What need is trying to be filled with these gadgets? I am at a loss to understand why they exist...