So when he bottle arrives from Germany, I shall check if it has Pi stamped. That's fine.

The small bottles, may have been a dud buy, but I can use them as practise bottles for my own use which is ok.

The thing that started it off was reading a long post on scuba forums saying U.K. Companies would not at any cost test certify or fill a DOT bottle from the US, which yes relates to scuba gear, but it's still a bottle.
Hopefully a nice place will be able to check these, but anyway, at effectively at £7.50 a bottle, I can't complain much if I can't use them at all or restricted to personal use.

Now I need to get my regulator and systems will be up and runnin! Aquarium regs?