One of the main concerns is the injury at the injection sites. Micro injections are really hard on living cells. The more dilute the solution, the less phytotoxic reaction you get, and the better coverage up in the tree you get.
Using fungicides were you repeatedly inject, like for DED, you want to use a macro-injection. It takes more equipment and time, but you want the best.
The other consideration is injection site locations. The best place, for several reasons, is in down on the lower root flare. You have to dig with a trowel or air spade to get there.
Tools like the wedgle, that use a small injection hole sound great, you know, small hole, small injury, but the phytotoxic damage turns out to be a large injury, and right on the trunk.