This could rewrite a few business models...
One of the sneaky little secrets about the propane tank exchange business is how full the average tank is when it is exchanged for a full one. Most consumers just don't want to take a chance on running out in mid-barbecue, and hence half-full returns are the norm.
It's kinda like buying the whole tank of gas when you rent a car. What a stroke of marketing genius!
Anyhoo, all that could change with transparent 20# tanks like these:
Of course, why would any propane company want to switch to them?