I've been on methadone for almost 20 years. I'm fine with it.
There is the constipation, if I don't get enough exercise, it's easily dealt with.
Also, if my dose wears off, I DO get pain, and probably some sort of reaction that's over and above the normal CRPS pain. I was told to think of it like Blood Pressure medicine, I'll take it forever, or until something better comes along. It's remarkably inexpensive too.

I do take Cymbalta and diazepam, along with migraine meds.

My pain is more than crps.

Wish you luck with your decision!

Pete