best I know are that copper mines are pretty nasty. I doubt that the chinese are, or can be, a lot worse than your favorite raw material western capitalist.
I don't know how nasty copper mines are in comparison to other mines, so I can't comment on that. But given the disregard of the safety of their own workers at home in China, I can't imagine them treating African works *better* than a western capitalist would. Of course, that would mostly be due to the western capitalists having significantly different safety standards depending on country of operation more than the Chines lack of such.
But I really like the claims of surplus electrical power and training the locals to run things.
Certainly there are benefits. Not saying there aren't any. After all it creates jobs as well.
As far as roses in africa, I believe you and I suspect it is stupid even from the get-go, but if I were to look closely I would ask how desperate the local government was for hard currency and why.
I don't think roses would necessarily be more stupid than any other crops for export just because you can't eat them. But using land that could be used to feed the locals obviously raises some questions, and dumping chemicals into the local environment clearly sends it over the top.
Another thing I was told in Ethiopia was that what had happened (simplified) was that after centuries of European rule, and decades of guilt based (and ineffective) aid from the West, locals saw the Chinese as an interesting alternative for building their nations. However, after about a decade of massive Chinese involvement, they realized that the Chinese were actually worse than the Europeans in taking the actual resources for themselves, while leaving minimal positive impact. (Also, by now better and more sustainable ways of improving standards of living has been figured out, though they of course are not without problems of their own...)