In regards to your methylcobalamin:
Only about 10mcg is absorbed on a good day from this at the 1000mcg daily dose.
That is not enough methyl stimulation to do much damage, as it has to be diluted in the whole body.

Injections however, release far more methylcobalamin and in some cases doctors give them daily or weekly depending. That could become a methyl load quickly. This is common in the autistic community, for example.

Since you have a mixed MTHFR mutation you cannot methylate well yourself. So if you use hydroxocobalamin, it may not get activated as much as you need it to be. So I would consider that.

I think your first attempt should be to avoid food sourced folic acid and to start Metafolin at 800mcg a day, and watch your reactions. You can increase slowly with time if need be. But very high dosing of methylfolate can be very stimulating and disturbing to some people. Best to start small, and see what happens.

In regards to your links to the vits....
They are very expensive. Solgar's Metafolin 800mcg is
http://www.iherb.com/Solgar-Folate-A...-Tablets/13961
A third the cost. Solgar is a well known reliable company.

Hydroxocobalamin tends to be pricey. You may not find much of a variance with it therefore from company to company.