I fail to see how powder is less likely to be tampered with than pills. Much powder is crap as are many pills, but with powder the potential for adulteration stands with every hand who handles it. Not so with pills. To tamper with pills you either have to shave or tumble them, or repress them. But altering the shape of pills can reveal this form of cheating, simply by comparing or weighing, and repressing can't be done by everyone.
As for purity?
Some time ago I was approached by a stranger and was offered a small amount of MDMA crystal/powder to test, said to be locally produced. It reacted violently forming a dirty brown/purple color with Marquis, a similar color with mandelin, a positive to Simons (blue) and negative to robadope. Using the permanganate test for alkenes, it was determined there was unreacted safrole/isosafrole present. I didn't do a ketone test but I betcha there was ketone present (more toxic to the liver than safrole). It was verbally confirmed that no distillations of either ketone or freebase were carried out.
The way I see it, any consistent pressor of pills is likely also to have a choice as to what goes in them. With the usual selection around (powder being much easier to import it is said), the above product would likely have been rejected by big pressors unless it was either very cheap or there was a drought.
How many caps of powder do you see with ~80-120mg of white, non-smelling powder in them? They're nearly always topped up with milk powder or something similar. Incidentally, even the washed product mentioned above - which I didn't see, but was described as being pure white in colour with no odour, and the roll was super clean etc - would still not be considered pure enough for human consumption IMHO. While such washing may remove much of the colour, lots of things remain which are still impurities.
One has to ask therefore, how much backyard powder/crystal is being produced without the lengthy distillations involving vacuum and other fiddly setups? Probably a good portion of it I would think. When considering this, I think it makes a well known brand of tablet a much safer bet, as production would have likely involved large batches produced using commercial pharmaceutical plants with dryers, large mixers etc, and for which distillation is automated and merely another step in production.
