[Stoves] coal briquette stove

[John Davies]

A friend sent me this:

A claim is made that a holey briquette costing R2   ( US$  0.28 ), burns for
10 hours.  Well I do not suppose much more than 500 watts would be given
off.

Haven't seen it before, any ideas ?

John Davies.

There's a guy selling mbawula's, and it looks quite well made.  No smoke?
Are you aware of it? 
http://www.bidorbuy.co.za/item/30800390/Imbawula_Stove.html