You make good points about the possible risks of using not just Android but any for-profit company that may have ulterior motives (such as farming and selling data). And in an ideal world we could develop something both cheaper and better than Android (not just OS stability and quality - but much more importantly available applications and dedicated hardware makers operating at scale).
An attempt to produce an African alternative is admirable. But it is also costly and highly risky in competing against the scale leader everywhere from North America to China. Cellphone penetration exploded in emerging markets, with huge benefits, not because someone developed special cellphones (either hardware or software) for Africa or poorer countries, but because as scale built up in developed countries it drove costs down to the point that it became affordable in Africa too. The same will likely be the way forward for larger computing devices (i.e., tablets).
"I don't look to jump over 7-foot bars: I look around for 1-foot bars that I can step over."