Re: DMPS vs DMSA, safety?
Please consider how many of the DMPS Backfire stories say that the person was chelating while they still had silver fillings in their teeth (and many others who do not say clearly whether or not they still had). That is extremely dangerous and the biggest mistake people make with chelating. A "backfire" would almost certainly have happened no matter what kind of chelating they did.
This is a good example of "improper chelating." The fact that a doctor gave this treatment without having the patient replace their fillings first is a sign of the widespread ignorance which health care professionals have about chelation.
As for what chelating method is best, using DMSA, etc. or a more natural approach, my philosophy has always been, "whatever works well for you." By all means, try the natural chelators and let us know how it works for you.
I would be very careful about too much experimentation though. Chelating is not 100% risk-free. It's usually better to stick with a method which other people have used safely and effectively.
BTW: You can get DMPS and DMSA without a prescription.