I wish I was as enthusiastic about the outrunners. To me, they are quiet....and that's where the advantages stop. The adjectives that come to mind for me are heavy, not-so-powerful, can't swing a very big prop for the current draw, etc.
We were discussing the 2814/XX vs the Lehner 1020/15 geared. It weighs 4.6 oz (bare motor) and delivers 110~200 watts (I'm hoping that's watts to the prop..) depending on the prop used, with 11X7 being the largest recommended by HL. My motor/gearbox/prop/prop adapter/esc/wires weighs less than the 2814 does bare and gets at least 250 watts to the prop, 335 watts gross, and will swing a 12X6 APC SF faster than HL claims the 2814 will swing a 11X7 (they don't specify what brand or style).
The AXi might be less expensive, but I'm kinda looking for performance. The Cobri gearbox is not noisy like a GWS is. Maintainence..not sure, spur gears ar $3.50 or so.
As for the B20 15L with the 4:1 planetary gearbox. I have never figured out how that combo got to be so popular. I mounted a B20 18L in a Cobri gearbox and geared it 4.86:1. It spins the same APC 12X6 SF I run on the Lehner 5500 RPM at 17.5 amps, 185 watts. Just perfect for a plane like an Attitude on some 1500 Tanics.
The B20 15L 4:1 struggles with an 11X4.7, and more current draw than the B20 18L set up I have.
So I'm not totally anti-outrunner (I do own a couple of Axi motors) but if you are looking for performance, a properly geared BL motor will do pretty good compared to an outrunner.