I have used it as a cover crop in my garden, never grown it to maturity and harvested, no. I think it does improved my soil. This year I let it get a couple of feet high instead of a couple of inches, we'll see if any grows back next year.
As far as quality of flour, I prefer electric. If someone knows of a hand grinder that makes a fine flour, I may be interested if it isn't at the price of way more work, it's already enough.
Flax is soft and high in oil, so if the grinder can grind it directly like mine can, or can't directly but can take a little mixed with appropriate grains like my whisper mill can, then in a hand grinder it makes it much easier to turn. Between being physically soft and high in lubricating oil, it saves on the arms. I think my grinder is called Back to Basics.
Being somewhat gluten free myself and dancing around the wheat and storage issue, I have had brown rice go rancid in around a year, so I just try to keep that rotating. Flax, I should have thought the same thing and it makes sense that it would, but I have not noticed any rancid flavor at all. I bet mine is a year old, give or take a little. For me, although I like it, a little also goes a long way. I only bought 25 pounds to start. Flax oil will go rancid very quickly, but it looks like stored in the original packaging it is good for a little longer. You'll have some pretense of 1 of the 3 Omega 3 oils in your food storage this way too along with other benefits. Sprouters can sprout this, but I only tried once and they stuck together in an unuseable clump, so I'll have to try another strategy next time.