Sufficient for rock, or should I add another 110 cab?

I'm thinking of having this horn sub built for use on my rock gigs.
I know some guys will think I need to go larger to cover larger gigs, but I'm thinking it might be enough.

What do you think? Should I add another 110 to it? Or is it enough on it's own?

Here's the complete site showing the build details...

Cute Little Horn Sub

Here's one pic of construction...

 

Oh, I know it's nothing new. I wasn't posting it as some kind of newsflash. I'm more interested in building one myself, but I'm just wondering if it will work for rock music on it's own or if I need to add like another 110 to it. Maybe I need to get a 210 or 410 to go with it and stack them? Or would that cause some off axis problems?

Would I be better off just using it alone and putting it on it's side or should it go vertical? I hear that vertical works better.