That's my whole issue with growing a tree from seed "the way nature intended". If you invest time, effort and most especially garden space in a mango tree for years and years then find out it's not a good producer, or the fruit is not tasty, what a waste.
Buying a grafted tree of a cultivar that you know is good, and that will fruit for you in 3 to 4 years beats the odds for me.
Bagging the fruit doesn't help me a bit, sadly. Insects aren't an issue on mango here. Squirrels are my biggest competition for the mangoes, and they just nibble the stem, let the fruit drop to the ground and they can get into any bag short of a steel mesh one. I found after trying all sorts of scent deterrents, motion scarecrows, fake owls and everything that the best defense was just to walk out there early in the morning and pick up the fruit on the ground. Then through the day I go out about every couple of hours and 'police' the area.
