The vBulletin version SMC has is "broken", and the "upgrade" isn't much better and also cannot do many things natively like Xenforo can. Xenforo was written by a bunch of folks who left the vBulletin team a few years ago when they got tired of all the problems. It's more stable, more extensible and pretty much works the same way from the end-user standpoint. No worries. I've already been through this conversion at another site I help moderate (different topic) and it went smoothly. And folks had pretty much instant, native support for the kinds of devices that they use today to interact, unlike with vBulletin.