I think if you keep them in an air tight container they would last long enough for week trip. That is after the first check drain the balloon and seal it thus not allowing it to be exposed to atmospheric conditions. Lawrence made a similar device for compressors that was good for several months.
FWIW the way they can be efficiently used for a group is to simply to fill the ballon with a bit of air from all of the cylinders. If activated then at least one cylinder is suspect. If not then dive away. This technique is faster than testing each individual cylinder. I think they fill a niche for a group of divers who want to check but not have the expense of an electronic unit.
And of historical note the above technical was used in WWII to test soldiers for diseases. Blood samples from say 16 soldiers were mixed together and tested. If positive they would split into two batches of 8 and resample. One sample would positive and the other typically negative. The negative group was the disease free. The positive sample was then split into 2 groups of 4 and tested again. The positive group would be continually split and tested until the one solider with the disease was found. This technique is call a binary search and is faster and cheaper than testing each individual. Especially when the chances of find a positive is slim.