I don't see the point in this Last touch detailer/spay.
Use a cheap sprayer with some warm water in and a dash of your shampoo, I'm talking a tiny dash. Works perfectly when claying!
Last Touch can be bought for about £20 for 4L, which makes about 8L, its not exactly expensive, and does a great job for a lot of things, claying, aiding when drying, occasional detail spray, etc. Obviously can do that with shampoo, but you don't get the same consistency I find.