You can commute on pretty much anything (seriously there are a ridiculous amount of options) and mountain bikes make great commuters. Thats what I use for my primary one. Its nice to have a 2nd bike (I have alot mroe than 2 bikes) when yours needs repairs or you wan tot do different type of riding or just want a change of pace.

So basically get something you will like and willing to commute on if you want it to have that function. For just a bit more money I think getting one of those BD bikes with an IGH would be better than just the singlespeed, but either way its tough to go wrong with any of those bikes at those prices although you will be paying a bit to have them assembled which is good that you are supporting your local LBS.