I don't actually know for a fact whether their firmware is trustworthy, but the fact that they put being Free Software front-and-center as a feature instead of forcing you to flash it yourself if you want OpenWRT makes me inclined to trust them more than I would any brand that doesn't do that.

(I only own one GL.iNet product -- a Mango v2 that I impulse-bought because it was OpenWRT and cheap -- but if stuff like the GL-AP1300 had existed at the time I was upgrading my network I would've gone with them instead of TP-Link.)