Well...at least they were free...I really can't find much of value on them either spec-wise, except some generic specs and a too-low-to-be-any-good price of about $30. Stagg music is more of a budget guitar/bass company you find in Walmart, etc, not known for selling mics. Which means these are basically cheap re-branded Chinese-made toys intended for kids and karaoke machines that some well meaning souls see as a great deal for "professional" equipment. Sadly, if they have to put "professional" on it, then it usually means it isn't.
This mic model's output impedance is unusually high at 1000 ohms, you normally would expect 150-300 ohms. Why does this matter? Well, to get proper signal coupling from a microphone or instrument to a mixer or amp input, you typically want the mixer's *input* impedance 10x the value of the mic or instrument going into it. If the Behringer mixer is anything like my Mackie's (probably so, since they copied a lot of their designs), the mic input impedance is generally around 3000 ohms, so would like to see 1/10th or less of that in a mic, i.e. 300 ohms or less, which this mic ain't. What's the effects of that? Well, besides possibly having issues with long cable runs (i.e. through a mic snake from the stage back to the mixer), most noticeable would likely be not being able to get as much volume level out of it as a typical (real) professional or even "pro-sumer" mic would give you, meaning you have to turn it up more on the mixer channel, resulting in more audible electronic hiss...and I gather that mic probably puts out more hiss to begin with by virtue of its cheap build quality. I had a cheap Samson mixer once that I bought just for basic on-location videography sound and it had so much electronic hiss I had to return it.
This isn't to say that these mics won't work for something, but I wouldn't do anything critical with them...maybe pass-around testimony mics, kids' skits or something? As a church tech director, I really cringe when people donate equipment rather than funds to the church's tech ministry. If they knew anything about what they were buying, they'd probably be *on* the tech team, but you really can't refuse it or you'll hurt their feelings...and after all, they mean well.
Hope this helps,