I have never used any of Chief's in-wall mounts, but have several of their desktop monitor arms, as well as a wall-mounted swing arm for our LCD TV, and have never been disappointed by their quality. Chief mounts just work- smooth joints, plenty of adjustments, accurate weight specs (i.e. mounts will actually hold their rated weights without droop), and solid construction.
Ergotron is generally consumer-oriented, while Chief caters to commercial/industrial applications.
Didn't look at the link due to a redirect, but are you talking about literally putting the TV in the wall so that the screen is flush with the drywall? I would think that the very first thing to consider would be the spacing of your studs and whether you would be breaking any building codes by chopping holes or notches in the studs to fit the TV.