Barry,
Mpingo is one of the few tropical hardwoods that I have a reasonably good knowledge about as I did some specialist study of it when I was doing my degree.
More serendipity!
It's use in musical instruments came about because of the increasing rarity of true Ebony, and it is sometimes marketed as such, though it's in fact a completely different species.
The instrument trade has depleted stocks of naturally occuring
Dalbergia melanoxylon - East African Blackwood and it's only in recent times that there has been an interest in growing it commercially.
The trees themselves don't grow very large and they have fluted stems & quite a lot of occluded bark. Like this...........
So that means finding a log which meets the quality standards and yields a reasonable amount of timber is hard. You can't really tell what sort of quality the timber is until the tree's felled. This means there is a lot of waste - made worse by the fact that they only want the deepest black colour. The tribes that live in it's natural range use the timber for carving ornamental goods & do not have the need for such high quality. A single tree can keep the carving industry of a given village going for months, so their use is rather more sustainable.
It's an incredible timber, being so dense that it won't float & can be machined like steel. The guys who fell the trees for carving have to work in teams of three - one guy banging away at it with an axe, one guy resting after his exhausting spell at cutting & the third guy sharpening the axe that's just been blunted!
If you make charcoal from it and try to cook over an Mpingo fire, it will melt your iron pot, so high is the calorific value.
Instrument grade Mpingo sells for ~$15,000 - $20,000 per cubic metre as a log & ~$44,000 per cubic metre as sawn timber. Compare this to UK Pine or Spruce logs selling for ~£30 and maybe £1000 for exceptional quality hardwood for the instrument trade (such as 'fiddleback sycamore' which gives what guitarists call 'flamed' figure).
I can't comment on the effect of it in hi-fi as I've not heard the products in question. However, I think there are plenty of other woods that would have a similar effect to what the likes of Shun Mook are touting for Mpingo.
But what's more important? The survival of the species in it's natural habitat or the musical gratification of a handful with more money than sense (and ecological responsibility)? I know which comes first for me & I think the use of it in instruments, and especially hi-fi, is criminally frofligate & it should be stopped completely from non-plantation sources. If plantations are managed by the carving tribes in a participatory forestry management arrangement, then we can all benefit. - We get the wood at a lower price, & they get the income from us.
As things stand at the moment, who can blame the villagers from felling their wild trees to sell the wood to the white man with big wads of cash in his pocket?
In the case of instruments, the use of Mpingo is purely for aesthetics & kudos - almost any dense wood will do the job equally as well. In an instrument without a reed, it's the column of air within the tube which is vibrating, & not the wood. It's been suggested that a concrete flute sounds the same as a wooden one!
See this link for a lot more on Mpingo in participatory forestry:
http://www.mpingoconservation.org/index.html