*Microphones are very subjective. Some microphones that work for some brilliantly may be disastrous on others. It is therefore important to understand the context in which this review is written and take it with a grain of salt, like all reviews on microphones should be treated.*
Let's be realistic. I'm not even going to criticize the quality of Behringer just because I know it's a cheaper set of microphones. I'm going to simply go off of what I have observed as a performer, and it is this:
These microphones are not great, but they are cheap, reliable workhorses that will work in a total pinch. Other reviews do mention the mic was a bit too bright and with a lack of bass, but I find that while these are true, there is a crippling 'dullness' that plagues the tone.
It's nothing one would notice when listening to it on its own, but pair it up against the standard SM58 and you'll realize that even if the SM58 does have a bit of a reputation for being honky in the midrange and dull sometimes, the XM1800s makes the SM58 seem sharper than a katana.
It's like doing a mix of Feeling Good, accepting it, then going on YouTube and listening to any one of the other nine million famous people to ever do it. Then you realize your mix sounds absolutely dull! Oh. Wait. Sorry, I was just moaning about something I did a few months ago.
At any rate, the XM1800s is okay in a pinch, but I would never use it in the same show as any well-respected industry-accepting microphone like the Shure SM58. It would just sound embarrassing. So I'll say this: if you're going to use this microphone don't use it alongside anything better. As long as you adhere to this rule, the XM1800s can take you quite a long way.
But if you can get 3 mics for $30, you could be doing a LOT worse.