OK so I had a chance to look at 4 hedgers this week: Stihl, Shindy, Husky and Maruyama. The dealers were very helpful and allowed me to try the units out.
There seem to be two types of gearboxes in articulating hedge trimmers, one is good, the other not. The first type has 4 gears and a bulky "pipe stub" housing whilst the other has 6 gears and a lower profile.
Case in point with Maruyama: since I already have their 40" unit which I am super pleased with, my expectations were high. The demo unit was a dedicated pole hedger with the familiar 22.5 cc engine (which is great). It comes with the bulky 4 gear box and let me explain why these boxes suck. Each pair of pinion gears is a reducing drive, that is a small input bevel and a larger output with more teeth.
The problem is the larger gears result in a bulky and heavy housing, and more importantly a higher twisting force (torque) on the articulating joint. To overcome this, the angle adjusting mechanism has to be stronger, a lot stronger. In the case of Maruyama, to adjust the blade angle, you need to: 1. stop the engine, 2. loosen a large knob, 3. lock the gears with a small lever, 4. adjust the angle with the handle 5. line up the teeth on the joints, 6. tighten the knob and 7. release the locking lever... horrible
A similar issue with Husqvarna's 327LD, which is a split-shaft trimmer with a hedger attachment. Again the box is bulky and the adjustment only marginally better. Here you have to undo a winged nut, the blades then annoyingly want to fold down, you adjust the angle (handle) and tighten the nut so squeeze the joint solid. Better but still not impressed.
Stihl on the other hand (HL100K) is quite good. The box has 6 gears, 4 (1:1) to get the power to the head and a final reduction set with lobes to drive the blades. Because the articulating joint is not a reducing drive, the torque going through it is small, thus the adjustment mechanism can be lighter and more user friendly. No knobs here, just pull a sleeve, adjust the angle and let the pin slide back, simple. By appearance Stihl's box seems to be the toughest of the bunch, but also felt the heaviest.
And finally the M254 Shindaiwa with hedger attachment. Like the Stihl it's a 6 gear box with final reduction drive and really low profile. I like the adjustment on these the most, since it can be done one-handed (unlike the HL100K). I don't think it's as sturdy as Stihl, but it felt the lightest and should be a winner in terms of productivity.
Overall I'm getting either Stihl or Shindy, but Maruyama (at least for me) was a big disappointment.