Is primrose oil any good?

Evening Primrose Oil's main use as a supplement is for women to mediate some of the effects of PMT/PMS. The research supportive of its effects in this regard is not strong. So it likely has little, if any, effect on women's moods and its effects would be even more doubtful in men.

There is currently no good evidence that it helps burn fat, build muscle, improve performance, etc so if you had another effect in mind please let me know.

If you are thinking about using it as an essential fatty acid supplement, fish oil (with a high concentration of EPA and DHA - if anything with slightly higher EPA content - is the best source of essential fatty acids for health and with mild effects on improving body composition and recovery from exercise due to its anti-inflammatory effect.

Also fish oil makes the blood platelets less "sticky", which may decrease blood pressure. So along with salt and excess carb restriction, this may have a mild effect on your mood. The best therapy for mood is likely behavioural therapy or meditation though.