VFD or gearbox for Linear Actuator?
VFDs can easily get a motor to produce full torque at any speed from full speed down to zero. The difficulty is in motor cooling. An inexpensive standard motor can probably not operate continuously at much less than half speed without overheating. It is generally always better to use fixed gearing so that the motor operates at full speed for the highest machine speed that is required. Use adjustable speed only to reduce from the highest machine speed to lower speeds. Don't use a variable speed drive just to operate at a reduced constant speed.

For 1/8 Hp, a DC speed controller and a permanent-magnet DC motor or even a commutator DC motor will probably be less expensive than A VFD. DC motors can also have difficulty with continuous low-speed operation.