I think these usually go for £200-300 in good nick. At which price, if you can deal with the hassle of bulk-fill, they are a bargain. About what the springers they replaced cost, but a generation ahead.

The cylinders have an official “shelf life” after which FWB say they should be tested and if needed replaced (10 years?). So I’d imagine those are officially out of date, and the corrosion would give pause for concern. I’m afraid I don’t know if replacements are still available.