How much prior psychedelic experience do you have?
I never tried psychedelics when I was young, because I had to start risperidone due to a mental breakdown when I was about 22 and I was always under the impression that you can't get high on 5-HT2A drugs when you are on atypical antipsychs... I only used DXM (and sometimes diethyl ether by inhalation, so all NMDA drugs). About 18 month ago I tried ingesting 5 grams of these seeds (obtained from the same source) and I was surprised when I got a nice buzz from them. Apparently those atypicals block only one subtype of the 5-HT2A receptor, and if you take psychedelics you just don't see any visuals, but the mental "mind-fuck" effect can be very strong despite of that.
I haven't had any signs of psychosis/paranoia for many years, and I've kept using neuroleptics mostly because I'm kind of dependent on the antihistaminic sedative effect to keep my sleep rhythm at least remotely normal and to help with anxiety. Therefore I think there should not be a very high psychological risk with these experiments. Actually the effects of those seeds was so fun that I really don't get how someone could freak out because of them. I only felt a little depressed at the come-down, but after sleeping for a couple of hours that depression went away.
I'm not planning to take psychedelics very often, 2 times a year at most. In fact I'm thinking of planting some Trichocereus cacti now, so I'd be able to dose some mescaline next summer...
EDIT: By the way, a thing I noticed with those seeds, if you mix them with a little baking soda before chewing, much like coca leaves and chewing tobacco are mixed with an alkali to get them absorbed faster, you don't really feel the bitter taste because the salty soda taste masks it.