I'd suggest you get 2 bottles in any case (if it's in your budget). I always found myself bringing in a 1/3- 1/4 full bottle for refill just so I wouldn't have to stop in the middle of the next job to slog down to the gas vendor because I ran out of gas. I ended up buying a small bottle to set aside the big one. Which also made it easier to work on remote jobs with the small one.
Of course, it depends on how often you expect to need a refill since the bottles aren't cheap... And in my neck of the woods, you paid a flat rate to refill the bottle, regardless of how empty it is. YMMV.
