Gemini inner tubes
I have used these tubes in the resuscitation of my old 5m Tornado. They are easy to fit, although the top tip is to use some talculm powder to get the inner tubes in smoothly. They will also then fill properly to fill the tube.
The problem I had with them was that my old tornado had excellent quality PU tubes, but the glue had had it on the sun-exposed topsides. I left the boat with the inner tubes quite firm and went away for a couple of days. An unplanned heatwave then struck and the glue on a couple of seams gave way. Therefore, I had to reglue them. The plus side is that you do not have to worry about the repair being airtight. I think the 4 inner tubes cost me about £300 - probably about 10-15% of new tubes. If my boat was worth more than pennies, I might have gone for a re-tube. But this seems to be a good solution for me. If i hve more problems with the PU outer tubes, I might get Gemini to make me a new set - and use the current liners as they are removeable.
Hope this helps with your deliberations.