All of the folates improve depression. Methylfolate is more active for some because it does not have to be methylated in the body first like folic acid does. There are people with genetic errors, who cannot methylate folate and B12.

There is another that works almost as well... you may have it there: Folinic acid.

There is only one single source methylfolate in US... it is by
Solgar company. Merck previously was not selling it OTC here so it could make more money selling to RX only drug companies.

I don't know how much you should take. If you look up studies you may find doses. There is a warning not to take high dose folates if you do not know your B12 status. If you are low in B12
you can damage your nervous system by taking folate and not bringing the B12 up to normal.

Also DHA (which is found in fish oil supplements) is also very useful for depression.

If you Google both you will find many articles.