You can find orthopedic surgeons that feel both ways in terms of stimulators. However, there are prospective studies out there that have shown that stimulators do have a positive effect on fracture healing. Most insurance companies will cover their usage, thus they are pretty well considered main stream treatment, in specific cases.
As to whether one company's unit will work better than another's, is a matter of debate, and is probably not significant.
The choice of which stimulator to use is most likely based on cost, availability, and personal preference more than anything else.