By coincidence, I've just been doing a bit of browsing on these. I've spotted one with a blown thermoplastic polyester liner that contains a boss made from either stainless steel or aluminium and are then carbon fibre wrapped with epoxy resin to withstand rigorous use. Unlimited lifetime, apparently. 300 bar. 6.8L weighs 3.0kg and is £250 +VAT (excl. valve). http://www.ashsafety.com/cylinders.htm

Any opinions on these?