To qualify the motor I designed a 3D printed motor mount.

It's composed of a rotating pulley and two motor+shaft holders. With it,  it was easy to fix a rope and to try to pull "things".

The conclusion are:

• the motor can pull up to 300g with this pulley before stalling
• a safe weight should be between 200 and 250g
• the motor draws 40mA as specified and at full load and up to 60mA when stalling
• operation is safe when powered at 4V instead as 3V (specs). So a fully charged Li-ion battery can be used.