[Ronja] Is an opamp oscillator reliable?

[Karel Kulhavy]

I want to build an opamp multivibrator to power the onboard 48V generator. A circuit like 
http://hyperphysics.phy-astr.gsu.edu/hbase/Electronic/square.html

However I have a feeling that the Barkhausen criterion is not met anywhere. The feedback with capacitor has to have 180 degree phase for Barkhausen to be met. This can never happen because the low pass filter has phase limiting to 0 for low frequencies and 90 for high frequencies. However intuitively I understand how it's supposed to work.

How can this circuit work then? Any idea? Is this circuitreliable at all, then?

I would like to avoid circuits which fail under certain temperature, supply voltage,
or component tolerance for some people and work for others.

Karel