If you are someone that uses ground flax seed, also called flax seed meal, you might be aware of the differences in price.
Right now flax seed meal is about 3.19/lb us dollars. From the same company (both at our grocery store), flax seeds (unground) are $1.49. It's quite a savings to buy the seeds unground.
As with all seeds, nuts, and grains, these keep for a good long time unground, but once ground the fats are exposed to oxygen and slowly degrade, which can become rancid. If you've tasted rancid grain/flour, nuts or seeds, it is a bitter acrid smell and taste. Avoid eating rancid things. The oxidized fats have free radicals.
I also buy chia seeds, whole. We use them daily with flax. When I run out of ground flax and chia, I grind more. I take a pound of each, grind them in the spice grinder, mix them, and put them in shaker containers to use daily, the rest in glass jars to freeze.