I'd say 2 things:
AIM is not law. The FARs are the law.
The equipment to conduct the flight is required to be carried. No law says it must be used to actually perform the navigation.
FWIW, the above is a regular topic which has been done to death on US pilot forums over more years than I have been flying.
I wouldn't say that a handheld GPS is particularly necessarily good for this kind of thing, partly because most of them don't have an OBS mode.