I have actually used both @steemnaira and @airhawk-exchange

I can not recommend any of this 2 means of exchange because they do not run the same service...

With @steemnaira you send your sbd to the official account tho they are presently working on their website where you can easily transfer your sbd to your already created account on steemnaira.com and then convert it to naira tho not at a fixed rate...

And as for @airhawk-project, they act like a middle man in other to make sure of transparency...

The seller or buyer makes his offer or rather intention and the other party that is ready will chat with them all on the platform, when they reach an agreement, the seller sends SBD to airhawk-project once they confirm transaction, the buyer sends money to the seller, once the recipent confirms the money, @airhawk-project transfers the SBD to the buyer...