I very much doubt that the speckled 2mg pellets contain heroin. The whole "speckled pills=heroin" thing is just an urban legend as far as I'm aware. And in any case, I've tried the 2mg pellets and I'm certain they contain a benzo of some description, though I have no way of proving that it's actually nifoxipam. A couple of those (so allegedly 4mg) seemed about equivalent to 1.5-2mg of etizolam in strength but quite different in effect (much more muscle relaxation than etiz but less sedation, a bit less motor discoordination and slightly longer duration).
It's no urban legend it did happen, and still does with some RCs. Iv been told at the SMS that some RCs have been found to contain heroin. Heroin is really cheap to make compared to the cost of a lab and proper chemists.
I may be barking up the wrong tree but the brown speckles imediatly made me suspicious.
Also the effects you describe could be attributed to opiate like effects. Like you said it felt different in effect and had a more muscle relaxant feeling. That could easily be describing a mild opiate high.
Maybe I'm wrong about the heroin. But there is defenatly something dodgy going on here
PS. SMS stands for substance misuse service