Planar Harmonizer , Magic Circles and Planar Binding

The Planar Harmonizer gives up access all magic schools other than Conjuration, which means they cannot cast Magic Circles.
Planar Binding requires an inward facing Magic Circle to be drawn before it can be used.

Can a Planar Harmonizer instead use the magic circle class ability they get to replace the spell?
Because it seems funny that a class that specializes in conjuration magic would be unable to use an iconic spell from the school...

Yes, the ability works like the magic circle spell and can be used as such. It should also be noted there's no requirement that you create the circle under your own power; you can use a wand or have another party member do it for you.