So as I randomly leveled classes to cap, I decided to level summoner, force and techer on a single character, while using other characters for other classes. Meaning, since it's just alt leveling, I followed no guides and read no info. Techer has the ability to create 3 minute long shifta and deband via the Extend Assist skill, and I supposed, since the skill description doesn't mention anything about being main class only, that if I picked techer as sub class (not for a serious build. just to alt farm) that I would be able to use that on another main class.
But lo and behold, I picked summoner main and tech sub, thinking I'd get my pets those juicy 3 minute shiftas, but nope. They last one minute. The skill description does not make note of the skill being main class only. Guess for now I'll be sticking to force sub (quick fire charge) for farming while I decide to go for something more meta for sum (FI perhaps), as that will be the main class I'll make this farming alt for.
Anyway, just a heads up for others to not trust what the game tells you. If you want to make a serious decision, you must go out there and check guides from real players.