It says its glycinate lycinate, so it has a combo?I know a couple guys who go up to 800-1000mg a day of Magnesium Glycinate for severe stress/anxiety/insomnia/rls.
I agree 300mg is the starting dose, ramp it up and get a good brand. Again, I prefer Doctors Best. I buy the non flavored version in powdered form and I mix in in my orange juice every morning and it mask the taste entirely.
Also, Labdoor is an independent 3rd party website that randomly test products (Similar like Anaboliclab) and you would be surprised how much shit is out in the market.
https://labdoor.com/rankings/magnesium