I have, back when I was working on that project. While I don’t remember the exact measurement, it was not efficient at all. At some point I added a capacitor to each of the coils, trying to get resonant coupling between the two coils, which improved the performance considerably. The following video was one of my sources of inspiration:

and here is an explanation from one of the replies on YouTube:

This was an only for fun project, so no additional documentation was produced for. However, this circuit is a variant of the Mazilli ZVS driver, also known as the Royer driver, is a self resonant, push-pull, free running oscillator. Theory: “A Royer oscillator is an electronic oscillator circuit based on a resonant, saturable-core transformer. Each half of the primary is driven by a transistor in a push-pull configuration. When power is first applied, it forward biases both transistors. If both of them will be in on-state, they will just short both the transformer and the input source. But in practice the Q1 and Q2 will not be “ON” at the same time because their characteristics are never exactly the same. One of them, let’s say, Q1, will turn on more and the extra current flowing in that side of the primary robs the gate current from the other MOSFET via diodes and starts to turn it off. The voltage at source terminal of Q1 will be at near ground while the voltage at source terminal of Q2 rises to a peak and falls back down as the LC tank goes through one half cycles. As the voltage at source terminal of Q2 passes through zero the gate current to Q1 is removed and the MOSFET turns off. The voltage at source terminal of Q1 is now allowed to start rising and Q2 turns on. That MOSFET clamps the voltage at source terminal of Q2 to ground; something that makes sure Q1 stays off. This same process repeats for Q2 completing the other half cycle, and the oscillator continues cycling. A condenser forms an LC tank with the primary and the voltage proceeds to rise and fall sinusoidal. If it were not for that capacitor, the current would continue to increase until the transformer’s core saturated and the MOSFETs destroyed. In order to prevent the oscillator from drawing huge peak currents and exploding, L1 and L2 is added in series with +V as choke coils. The LC impedance is what limits the actual current (the chokes just mitigates current spikes). This oscillator is zero-voltage switching (ZVS), meaning that the MOSFETs switch when they have zero volts across them. This allows the MOSFETs to switch when they are carrying the least power. Being a resonant oscillator the frequency that the Mazilli Oscillator will run at is determined by the inductance of the transformer’s primary coil and the capacitor. You can use the following formula to figure this out: f = 1 / ( 2π * √[L * C] )f is the frequency in Hertz; L is the inductance of the primary in Henries; C is the capacitance of the capacitor in Farads“…