Of course the Muslim Brotherhood is unique in many respects, but I don’t see any reason why the truisms about organized opposition groups do not apply to them.
There is no question that they use their influence to control revolutionary activity, that they are more committed to improving their bargaining position with the regime than they are to overthrowing it; that they are infiltrated, and that they are absolutely tied to the existing power structure and to the interests of elites.
With regard to funding, there is no transparency at all, so it is anyone’s guess.
Officially, their funding comes from members, but this, of course, only accounts for a portion of their finances, probably a relatively small portion in fact. Their funding comes from wealthy members, from foundations and charities, from investments and from businesses. Foundations and charities receive a portion of their funding from individual donations, but also from grants by corporations and governments.
I am not sure how this would exempt them from the truisms I have mentioned.
As I said, these are applicable to varying degrees, and smaller groups are more likely to be infiltrated and controlled by the power structure, but larger ones are more likely to have their own vested interests in the power structure, so it works out to the same thing.