I'll be the opposing opinion. My last two batches using Coopers drops were foamy volcanoes (stored at 68F). I've since used those same bottles for other brews with no problems. I was bottling using two different sizes of bottles (16 & 20 oz.), one time. I guess-timated how much beer I had to bottle, calculated how many drops I'd have to use and dissolved them in two cups of water to batch prime. That turned out okay, maybe you can do the same on a smaller scale. One drop per "stubbie" (12 US oz.), 12 drops to 1/2 to 1 cup of water, boil, cool and prime.
I'm hoping to be heading to Brewtopia in Port Jeff, not too far from here, to give the Coopers kits another chance. Munton's also has carb tabs (?). I'm sure someone else will pipe in with some software that will be more accurate than my WAG.