Have you read the 5-mapb thread here? There are lots of reports of Serotonin Syndrome, albeit with a little irresponsible dosing, but it's looking to be much more dangerous than the APBs.
Are you located in the UK? If not, why not go for 5 or 6-APB?
The dose I've had in mind was about 100mg with maybe a 50mg re dose a few hours later. Without a psy, this never caused me any problems. Do you think this plus lsd (100-150ug) would be enough to have a risk of causing ss?
I'm not from the UK. The normal apbs are illegal here, but the MAPBS (and apdbs and eapbs) are legal. If 5 and 6 apb were legal I'd pick them without even asking. 5-apdb is just boring, the eapbs have reports claiming they aren't all that. Maybe 6-apdb, but I've never even tried this one and don't think I have a source.
I don't see any reason why it could cause Serotonin Syndrome because of mixing, when MDMA has been taken the same way without incident (rarely) so many times. Although maybe someone knows more than me... I'm purely speculating.