If buying secondhand its 'buyer beware'. If in doubt don't buy, but you can make savings by doing so in the second hand market - as long as you check the sums. Ensure you get to know the condition as well as thelatest test date, and born date / expiry date.
(Remember to factor in the shorter life and the potential that you may have to get it tested soon)
With second hand you have the option of getting it retested straight away regardless of the renewal date - this gives peace of mind, but at added expense.
Value for moneywise a £40 steel cylinder will go a long way compared to a fibre bottle. (You can buy a steel bottle every 5 years for less than the initial purchase of a fibre bottle).
Steels are cheap enough to not worry about getting tested at the 5 year stage, (By that I mean stop using it and buy a new one)
But if you arrange testing by handing over with no postage invloved they can be tested every 5 years at about £20 / £25 a go, and will last forever as long as they keep passing the test.
The advantage of a 4500psi fibre bottle is that most are bigger than the steel bottles, they hold more air at higher pressure and are much lighter. The disadvantage being cost and that they have a maximum life cycle of 15 years.
Depending on where you play you won't always get fills at 4500psi so won't always be getting the full benefit of fills, however unless you haev a small fibre bottle you will always get more air per fill then the acerage steel bottle.
There is also the option of Stako bottles. These do not have the option of retesting so have a more limited life.
