Even if the solvents you use are clean, they still aren't practically good for your health. Not that many are using DCM but I still don't like using naptha or heptane without some sort of hood.

How can the average person guarantee that the solvent they are getting doesn't have any traces left behind just because you can't see them with a naked eye on a piece of glass doesn't mean there isn't any there. The only I'm aware to accurately measure such a thing is with some sort of chromatography, which isn't cheap.

Yes you can get by with the basics and a clean procdeure, many do as have I. You can ReX and ammonia or carb wash all day long with great results. But there's something about d-limonene, call it a placebo, that isn't nearly as harsh and theres definitely more synergy to it aswell. To each their own but don't knock the orange peels till you've tried them side by side...