Well, you get used to the "7th" string. I wouldn't use it on stage when I only got it for about two weeks or something. You WILL definately make mistakes because you are used to the six strings and will play the 7th by accident sometimes...
Since you're in a band situation... Do you write alot of stuff for yourself or mostly for your band? I ask this because when I was in a band I didn't do much anymore except the work in the band, I didn't really have alot of time for my own stuff anymore.
Since the other guitarist doesn't have a 7 string (and bass player not a 5) you'll probably can't write 7 string tunes for your band so... In other words will you end up using it alot for your own work, that's something you should think about.
Will you like the 7 string? Well I think so... It's always fun to try new things and experiment and blabla.. It just keeps you busy as a musician and that's great. I don't have a 7 string mysef but I played a 7 string schecter ones and I wish to buy one in a few months. (Probably an Ibanez Xiphos).
IF you'll buy one: I would just buy a good one right away instead of a cheapo, since you probably will like it and end up wanting a better one.