There was a very long thread on Anabolic Minds regarding DAA safety. A lot of discussion back and forth which was quite interesting.
Seemingly, the take home message was that agonists of the NMDA receptor in the brain doesn't necessarily equate to excitotoxicity. The DAA side effects in the brain which have been suggested seem to make a tenuous link between the two which is where the confusion has stemmed from.
It would take a very long term study (decades, in theory) to judge if an ingredient had any detrimental effect on the brain in the long term in regards to excitotoxicity or degeneration. This is very unlikely to happen.
I have used DAA and haven't noticed anything in the way of brain fog. Some people have reported it and some people have even reported improved mental clarity so it is hard to deduce anything from it. Something I found interesting was a lot of side effects were posted when it first came out but appear to have dwindled off which could be attributed to placebo effect where people are expecting negative sides from DAA which leads to a self-fulfilling prophecy.