I only buy if a friend tells me of some new guy who is giving out 'fat wraps' i.e. above the 18% purity normal for the UK drug scene.
For a long time, a lot of HR experts have suggested that H will folk into 2 different drugs. The dirty brown freebase (smoking heroin) at the normal potency & effectively Number 4 which is pure diamorphine for snorting & shooting. The risk receded when the H manufacture began to be done in the country of origin. The average purity of Afghan smoking heroin is 78%... so HOW MANY cuts has it been through?!?
Even in the 1970s where, in big cities, asian dealers sold mostly to asian addicts but money talks and the guy I was with got 1/4 of each. He said the brown was 'warmer' (other alkaloids?) where as the white gave you a push to do things, as pure H does unless you snort enough to get a good nod on.
That was 40 years ago. I can imagine people mixing in dexamphetamine (to make a speedball) or cocaine (to make a snowball). I think they had less customers for the white 0 it was x2 the price and 99% vs 78% so, logically, the brown is cheaper but ladies (in particular) seem to love snowballs. Ladies, in particular (I don't know why) went crazy for snowballs. VERY destructive. That was the period when the MAJORITY of users were middle-class and £100/day was do-able.