I DO know mangoes and how grafting works. My Glenn is grafted, but flowering anyway, so I can only put the blame on the crappy, stony hillside dirt it is growing in. Mangoes prefer clay flats. Don't really need watering over winter, they are dry tropics trees.
The best mangoes I ever ate were commons. After school we would climb the neighbour's tree and only pick PERFECT fruit and drop the seeds under the tree. They are full of flavour and only got stringy if a little too ripe. Cold, eaten with a knife, not with juice running down your chops they are underrated. The BIG problem was the size of the tree.
