Yes, if you have a highly customized version with custom pages, thread bits, etc it might not be the best option for you unless you're willing to spend time or money on customizations. It's a very lightweight mobile theme that is flexible enough to build on top of. A lot of the features have been ripped out to focus on the core functionality of vBulletin. There are many free options other than vBMobile, but most don't work and are outdated.
vBMobile demo:
http://vbmobile.com/forum/