Bilateral aid straightens the bonds between given countries and through that provides a fertile ground for up keeping and better upholding international security. Some of the aid provided does run through already established channels and that does keep those links strongly tied together. Some countries as well are being accommodated for improvement of relations with others through these actions.
Yes, bilateral aid better upholds international security, because the aid is better tied to the giver. Aid has little to do with security. It might affect it a little bit, but ultimately weapons production and world power are more pressing issues of national security. The country receiving aid might not thank anyone if the aid is given multilaterally.