A buddy of mine started taking one of those thru-the-mail classes.
The books they sent him seemed to be quite informative and they'd also send him different tools once a month or something like that (kinda basic tools... feeler gauge, circuit tester, allen wrenches...)
He had a bike to work on as he went through the "classes" so there was "hands on" work he did. Just no one to guide him through the learning process, except trial and error on occasion.
Like any schooling, you have to apply what you learn for it to be any good
. So, IMO, mail order or online classes can be beneficial as a cheaper alternative to a vo-tech or MMI (Motorcycle Mechanics Institute) type school, as long as you put your mind to it and WANT to learn and excel
Granted, a shop looking for a mechanic may be a little reluctant to hire a mail order grad (not sure what kind of credentials mail order classes may give you) as opposed to an actual schooled grad, but that really all comes down to how well you sell yourself to the employer as knowing what your doing and being confident that you can do the work they're looking for.
As to my buddy, well, he ended up quitting the classes after a few months or so. He got a job at the machine shop I used to work at and started taking a Machinist's Apprentice class, was happy enough there to no longer persue the mechanics class. But he has mentioned that there was a good bit he learned from what he did complete. He also recently got his Journeymans Papers as a Machinist.
Best of luck, Stone, in whatever you decide on this. Your destiny is in your hands.