Unfortunately, I do not have any experience using an external fixator for this procedure. If the joint is not so bad, subchondral drilling seems to work. If the joint is really bad, then the surgeon should discuss arthroplasty with or without a joint replacement or fusion. The external fixator has many uses, such as lengthening bone and fixating where internal fixation is a disadvantage. It is somewhat cumbersome to get around on crutches for a length of time.
Can your doctor show you any published studies? Whether or not you fully understand the entire article, usually the conclusion would be understandable. If the studies do not have a number of subjects or the follow up is too brief, it would be difficult to claim this as evidence of success. Thjat being said, every surgery aand every surgeon for that matter owes a debt of gratitude to those who pioneered the procedures that are done now. Someone had to think of the procedure and others had to do them. Failures and successes had to be chronicled and further enhancements or variations suggested. So, in short you should decide what you want to do based on information and faith in your doctor.