With Algae Oil, the good thing is that a lot of stores now carry it. While the quality might not always be as good as it can be, they appear to be good overall. Without having to worry about mercury levels and various purification processes, you can have an easier time buying them compared to other sources of long chain omega 3's. If you want what is likely the best quality algae oil on the market, however, I would recommend checking out David Wolfe's Algae Oil from his David Wolfe Foods line. It is a raw, cold pressed, algae oil that contains DHA, EPA and DPA. DHA and EPA are the two that are often cited as being important, yet DPA is something that will likely be shown to have benefits. It also contains Astaxangthin which is a powerful anti-oxident. If you choose a less expensive approach, however, the various other algae oils on the market are likely good options and provide the benefits you're looking for from Omega 3's. They might not have the levels of EPA that fish oil does, however, DHA is likely what a lot of people are looking for when they buy Omega 3's. So essentially, Algae Oil are high DHA supplements without the toxicity associated with low quality fish oils.
DHA and Omega 3's in general are found to be beneficial for:
Nervous System Issues
DHA is suggested help rebuild the myelin sheath, which surrounds the nervous system and allows feel-good neurotransmitters to flow. While other vegan sources of omega 3's can be converted into DHA, this is likely not enough for some people due to the low conversion rate. Algae Oil is a good supplement for this reason.
People with excess anxiety, OCD, and other issues that are connected to stress or the nervous system might benefit from added long chain omega 3's like in Algae Oil.