Personally I think these devices are ... well they are like .... ummm well sort of like... hmmm... OK.. $ 8.00 refrigerator deodorizers - nice lil plastic containers filled with 1/2 oz baking soda.
What stasis point your new humi starts in has a big impact on how many of these you need. If it's summer and the humi has been in a non AC warehouse down south where the ambient humidity is 75%.... well it's probably over seasoned to begin with. If its winter in the north where it came from where the humiditiy is 25% you might need 2-3 times as many to get the wood fully seasoned. Lined with 1/8 inch cedar vs solid or thicker cedar is another variable which could increase time and or number of packets.
Generally speaking, if you don't use the "wipe method" on a dry humi you are looking at a ...veeery long time to season with any passive seasoning method absent a couple wipes, this and beads probably taking the longest.
A gallon of distilled, a dish and a couple paper towels = much quicker and cheaper. But .. it's simple one stop shopping to get these when you buy your humi so they found a niche which is the American way.