GBD Prehistoric With A Couple of Repairs- Smokes well or Junk?

I think it depends on how well-done the repairs are. . . which I'm guessing you really have no way of knowing. (But I've never smoked a pipe that has been repaired like this; others may have a much better sense of what to look for.)
The banding shouldn't be an issue. Many older pipes have had shank cracks repaired like this. Assuming it was handled correctly, it should essentially be as good as new. I'd be more concerned about the briar plug in the bottom. The only reason I can think of for that is a burn-out. But, again, assuming it was repaired correctly, the pipe is probably fine to smoke.
I'd personally be wary of this one, though, simply because it has had these two repairs. It seems like a lot of work to do on a pipe that likely wasn't that expensive to begin with. And I'm wondering just what the previous owner(s) put it through. Personally, I think I'd always look at it as a flawed pipe, and I'd likely only use it rarely. But that's just me.
Bob

I have one cracked/banded pipe and it smokes fine. I have no idea about a briar plug. Do you have a picture? I would be interested to see.

I've owned a few GBD Prehistoric pipes with the perplex stem and I found that new or on great condition they were ok smokers. They tended to get hot rather quickly so you'll need to puff really slow. But once you get the hang of them the are great pipes that's probably why the previous owner did what they could to keep it going.

Blue magic polish will clean that band up nicely also the perplex stem is pretty clean so I think you got yourself a nice pipe there just keep smoking it and buildings that cake.

I am right in thinking that someone in the past made a plug to fill up the hole at the bottom of the bowl? If so that has to be one of the cleverest repairs I have ever seen done to a pipe. Thats a great conversation starter if ever I have seen one.