I have had the pleasure of fitting these to a 5 metre Tornado.
They are easy enough to fit, just cut a small slit, fold the inner tubes as descibed in the instructions, pass them through the slit. fit all the inner tubes and then inflate them in equal amounts, slowly, then just glue a small patch over the top of the slit.
what the website or Gemini didn't tell me is when you inflate them, they have to be rock hard, the best way to describe it is when you think they are hard enough, just keep adding air until it is pysically impossible to get any more in.
I fitted them and inflated them as I would the tubes but on the first outing they deflated quite rapidly.
when I removed them the 2 rear tubes had rubbed against the inside of the tube near the transom and split in several locations, the same both sides.
Gemini did take them back and repair them at their expense which was good and explained about inflating them rock hard and told me they would put this on the website, i haven't checked but they may have now.
After I refitted the inner tubes and inflated them they were no bother.