The tanks are built in the EU and have TUV approval as well, as I believe, the UK. They have been used in Europe
for a number of years before getting DOT, in the USA, approval. The valve they have are the OPD valves. They are for overpressurization, supposedly they keep the tank from experiencing catastrophic failures due to overfilling and temperature drive pressure changes.
I have been using the things for almost two years now. They have been great. I threw out my steel tank becasue it was getting rather rusted. My aluminum tank is holding up well though! So, so far, so good.
I like that I can see the level of fuel
in them. I have lots of warning on when I need to top up. Most places I have been filling up at in the last year charge by the tank. You put 1 lb in, $17. So, being able to cut it close to the bottom is VERY nice. With the aluminum, I end up pulling it dry and carry a spare to make sure I am always covered. But, it is nice to know you're not going to have enough fuel
to keep the propane heater running the night, or enough to cook dinner for the folks that are headed over.