I bought the Arborjet system last fall, and have mainly used it for bark beetle control in ponderosa pine (before attack, in a few cases after attack). This spring and summer I'll see results from the 50 or so trees I have injected, as the Ips bark beetle outbreak will continue this year. Due to the lag in translocation throughout the phloem in big trees, it may take 4 - 6 to protect a tree from Ips bark beetle attack (they start in the top).
If I get a call for a pine being attacked within the bark beetle flight season (April through October) I may still climb the tree and apply a different insecticidie as a bark spray to the top (Sevin or dinotefuran). I bought the ArborJet system to get away from doing that, which is a huge amount of work: rig,climb, and prune out infested limbs and/or top; remove deadwood; return at dawn on a windless day, climb the tree in full rain gear, haul up a full back-pack sprayer, don giggles, mask, and rubber gloves, and spray; come down and wash all equipment including climbing gear and ropes, then hose down the drip area. For a large tree, I charged anywhere from $1000 to $2500, and did not make my profit margin.
Arborjet, expensive as it is ($200 - $600 per tree) is cheaper and takes a more predictable amount of time. I inject a mix of ememectin benzoate for the bark beetle and propiconazole for the blue stain fungus. The same products will control branch canker, pitch moth, and shoot moth, which are fairly common.