I eat large amounts of chia seeds. Started when I was looking for something with a lot of fibre to make up for the grains I wasn't eating any more, increased when I went more plant-based and was looking for protein, further increased when I started really liking them in coffee.
They are very nutritious - huge amounts of fibre, the biggest plant source of omega-3 apparently, high-quality complete protein, good micronutrients. But I don't think there's any real evidence of a particular T2D benefit, except to the extent that there's some weak-ish evidence that fibre can be helpful. I think it might have helped me when I was getting things under control, but it could well have just been weight loss at around the time I started eating them.
Flax seeds are similar, but you have to grind them & after which they can go rancid after a while, so more of a hassle.