I use their opticleanse and the 5-MTHF ES (methylfolate) supplements.
I don't have any issues at all with the methylfolate (but building slowly as per all recommendations). I'm currently taking 3 5mg tablets which is a pretty high dose.
When I take a break from things and start back up on the opticleanse, I have mild diahhrea, but it usually passes within a couple of days of taking it and then it doesn't bother me again.
I'm currently gluten-free, dairy free, low citrus, low soy... and cannot tolerate any greasy/fried foods nor any other forms of magnesium (except epsom salt baths) due to intollerances. I do think it's the very low amounts of magnesium that seem to cause me issues temporarily with the opticleanse - however, taking it multiple days in a row seems to help a lot.