The main problem with ALA is that to have the good effects attributed to omega-3s, it must be converted by a limited supply of enzymes into EPA and DHA. As a result, only a small fraction of it has omega-3's effects — 10%–15%, maybe less. The remaining 85%–90% gets burned up as energy or metabolized in other ways. So in terms of omega-3 "power," a tablespoon of flaxseed oil is worth about 700 milligrams (mg) of EPA and DHA. That's still more than the 300 mg of EPA and DHA in many 1-gram fish oil capsules, but far less than what the 7 grams listed on the label might imply.
https://www.health.harvard.edu/heart-health/why-not-flaxseed...
Also, beware of omega 6 fats. Seed oils (corn, soy, canola) used in commercial food products are incredibly omega 6 dominant in terms of polyunsaturated fat content. Consequently, the ratio of omega 3 to omega 6 fats we consume has plummeted as food production has industrialized. Omega 3 fats are precursors to generally anti-inflammatory signaling compounds, whereas omega 6 fats are precursors to pro-inflammatory signaling compounds. The bias in fat intake leads to more pro-inflammatory signaling in the body, and a lot of alt health types have alleged this is a major causative factor in the obesity epidemic.
This is important for depression, because chronic brain inflammation as a cause of depression was one of the going hypotheses at least a decade ago when I last looked into all of this. Upping omega 3 intake is an intervention that can address chronic inflammation, which is potentially why it improves some cases of depression.
Pretty much nobody in the west needs more omega 6s these days. I hear even farmed salmon eat primarily corn and soy based feeds these days, meaning their fat ratio is skewed much more heavily toward omega 6 than wild salmon and fish.
First, when taking omega 3 supplements, you generally care about increasing the ratio of omega 3 to omega 6. Hemp hearts have much more omega 6 than omega 3, so they're not very effective for improving the ratio.
Second, hemp hearts contain ALA, while what you generally want to improve is EPA and DHA (this is also covered in TFA). The body can convert ALA to EPA and DHA, but it's not efficient.
So all in all, if Omega 3 for the article's stated benefits is what you want, this is not the way. I recommend looking into eating more fish, or if you want a vegan route, algae-based supplements. [0] is a decent source from the NIH about foods and their Omega 3 content, split by ALA/EPA/DHA.
[0]: https://ods.od.nih.gov/factsheets/Omega3FattyAcids-HealthPro...
Flax seeds are even better just for Omega 3 at 1:3, but hemp hearts have other benefits, like more protein, which is why I called them out. That said, I eat a fair amount of flax seeds as well.
This is not to say that they're unhealthy of course.
EDIT: see the sibling comment by code_biologist, it's much more comprehensive than what I've written.