To be fair, it is not a legal requirement to but BS/EN rated extinguishers, but enforcing authorities will always accept them as being suitable & sufficient if so marked. For those reasons - and that buying firefighting equipment has never been cheaper, I would always recommend a 'compliant' extinguisher. I am interested: What type, and size are they? Do they conform with the coloured panel arrangements? How about servicing and most importantly, where are they from? All extinguishers are pressurized vessels - or capable of being so. And that is where the risk lies. An EN rated extinguisher will give the user confidence that it will operate and wont explode when/if its required. Unless there's a huge mark up to ensure reasonable returns, I wouldn't touch them

Capacities you quote are I think too small for EN 3 compliance. At least the product isn't making a false claim of compliance (some did in the past). EN 3 applies (to the best of my recollection) down to 1Kg and 2 litre capacities. The general presumption is that anything smaller wouldn't offer sufficient discharge in the event of a life-threatening incident (thus "not a fire extinguisher"). I take it you're in the supply chain. Why not have a chat with your local Trading Standards people? On a note personal opinion, given the modern vehicle construction standards, and unless your concerned with ADR - on the basis of risk -is a fire extinguisher in a modern vehicle really necessary?