If you can afford to buy a carbon tank than do because they are much lighter and will be better in the long run, but if you need a tank fast and cheap u could pick up a used steel tank for 30
That's subjective, and with regard to weight part of the 'light' reputation of fibre wraps is in comparison to older steel cylinders. Now the basic 3000psi 'steelie' is aluminium for about £30 new and the weight difference is not so profound
A fibre wrap is lighter than the comparable aluminium, BUT an average aluminium 3000psi is smaller than an average fibre wrap, so the weight difference gets closer
For true lightness you need to go for an ultralight fibre wrap cylinder and then you are looking at £200+ for the initial purchase
Compared to a normal fibre wrap at £150, with 2 tests for its maximum life of 15 years (£200 lifetime cost) aluminiums are better vfm for the air supplied and its life - even if you don't bother to retest and keep buying new
Bump it and chip the fibre wrap and it's now only worth going into the bin (unless it's repairable by the manufacturer and like a recent poster you're looking at around £40 plus courier costs to send abroad)
Bump an aluminium and it will laugh, you may just scratch the paint
Balance and ergonomics are more important than weight, get the right one to fit you
Fibres used to be the only option for a curved base which allows you to roll the gun in your shoulder, and aluminiums had flat bases. However now there is a curved base aluminium, which retails at about £40 new
Never spend £150 or £200 on a cylinder without researching