  The form factor of hadronic systems in various forms of relativistic quantum
mechanics is considered. Motivated by the agreement of the nucleon
``point-form'' results with experiment, results for a toy model corresponding
to the simplest Feynman diagram are first presented. These ones include the
results for this diagram, which plays the role of an experiment, for the
front-form and instant-form in standard kinematics (q^+=0 and Breit frame), but
also in unconventional kinematics and finally a Dirac's point-form inspired
approach. Results for an earlier ``point-form'' approach are reminded. Results
are also presented for the pion charge form factor. Conclusions as for the
efficiency of various approaches are given.
