Electic vs Ultrasound bone growth stimulation

Hello,
I am a 21 year old male and I hit a tree sledding 9 months ago and have had 2 failed ORIF of my left talus and navicular. I currently have severe post traumatic osteoarthritis at the talo-navicular articulation as well as a non-union of the navicular bone. I am going to have an isolated talo-navicular arthrodesis over Christmas along with an iliac crest bone graft. I have received contradicting information on what types of bone growth stimulator to use. I have had one OS prescribe an electrical bone growth stimulator (OL1000) which emits a combined magnetic field and yet another one suggest ultrasound bone healing system (Exogen 2000).
What are the differences in the two technologies and how can I determine which is best for my specific case?
Thanks,Bryan