I use the alesis 3630 with good results.
You will have to experiment with your settings. If you are recording live it will help out keeping the drums and other instruments out of the vocal mic. But if the singer backs off the mic too far you will loose that signal. I use it for singers with a booming voice and I find that limit where it cuts his/her signal. Set the pop screen and tell them that they cannot back off the screen. Then the mic picks up nothing but the vocals.
There are hundreds of compressor/limiters out there. Shop around. Ebay has alot to choose from. I bought my 3630 through ebay for $100 (us) I am very pleased with the unit
I could tell of other situations were it helped.