It sucks when manufacture do this and leave no reliable information about what performance the unit can actually do.

I have installed 2 of them, neither time did I put one on my bench and load test/measure for actual output. But I can say it is absolutely more than the 30-45 watts speculated in this thread.
One of the installs is running 4 rooms of in-ceiling speakers on A output. And some Triad outdoor speakers on B output. It sounds to have about the same power as the old SONOS Connect:Amp (@55watts per channel). So probably close to that. Sound quality was about the same as well, which is to say it's ok.
For the price, it's as good as any other cheap 2 channel stereo receiver out there from Onkyo, Denon, or others. It will do for budget offerings.

[edit]: One thing I do like about the Yammy that I don't think the other budget 2ch receivers do, is the programming of the volume levels just like on the AVR receivers. You can set the max volume and a turn on volume.