I've not yet ordered from those guys but have spoken to several of them... they all want payment up front.
John Mbugua with World Class Flies
seems to be the most honest and reliable. I checked several of his references and they all checked out good. His sample flies are very good.
Henry Mwangi claims he can sell flies in bulk for $2.00 per dozen. I got some free samples from him also and they all looked very good. I don't know anything about his dependability but he offers a long list of references. His email is firstname.lastname@example.org
Hope this helps.