The FE I use are checked/tested each and every time they are refilled, I would assume that as long as they pass the tests they can be refilled but I may be wrong.
I pay for an exchange service so its annoying when you take a nice shiny empty FE and get given a tatty one back that has clearly been around for a while
One of my 2KG has a twist valve fitted so I don't get exchange on that one it has to be refilled.
Mines not quite ready to be refilled
don't tell me you have almost used 5kg of Co2 already!!
It's a good ideal to have a spare full FE that you can use when yours runs empty and the other is being refilled. Just contact your local FE companies and ask for quotes for re fills. The prices will differ a lot from one place to another.
I pay £20 for the 5KG to be refilled and £12 for the 2KG, This is with a company based only a couple of miles from me. I know it can be done for cheaper but not without having to travel further away.
And don't be afraid to haggle