Private provision of police services in Tanzania

It has been brought to my attention, by a friend who has lived there and knows the country, that police services in Tanzania are mainly provided privately, by a few competing firms. Corruption is low, which is to be expected when there is experimentation on a free market, and these firms have not deteriorated into warring gangs. I know very little about Tanzania, so this information is possibly inaccurate, but a search on Google turned up an interesting book on the subject. Perhaps this is more evidence for a positive case for market anarchy, like medieval Iceland.