Yeah the risk is pretty minimal as there is only a very small amount of gas in the system with Hychill in the event of a leak due to a failed seal it will most likely leak out very slowly at a rate as to be unlikely to pose a problem.
A quick loss of gas due to a crash or some such, will be very cold and unlikely to ignite before it’s exhausted and dissipated.
You have a greater fire risk from the petrol.
I really couldn’t say much about R290 or R600a as I’ve had bugger all to do with them.
I gather you in the UK, as far as I can tell the are distributors in both France and Spain, but not the UK.
It’s even available from Amazon here, dunno about about elsewhere.
It’s much cheaper than R134a so that’s a tick in the + column, as is the fact that due to lower pressures required there is much less load on the compressor which will pay dividends in power savings, longevity, economy and less likely hood of leaks
You do need the usual AC equipment to use it, such as valves, gauges, hoses, vacuum pump etc.
"Keep calm, relax, focus on the problem & PULL THE BLOODY TRIGGER"