I always recommend an aluminium/steel cylinder for a variety of reasons, fibres only if you have the funds available and not for the commonly used reasons
Initial outlay is £30 to £40 compared with £150
£150 must be considered an investment into 15 years, but to get that 15 years life would need two tests - if you get a good price on these and don't have to post the cylinder back & forth then they are in the region of £25
That makes a fibres lifetime cost about £200 over 15 years
A steelie tested twice will cost £80 to £90, or if you throw away and buy new every 5 years that's £90 to £120 for 3 cylinders
But the steelie never expires so if you test it then you get 35 to 40 years for less then the fibre life cost
Moneywise the steelie wins everytime no matter how you calculate
The falacy of fibre wraps are that they are lighter and have more capacity
They are lighter and they do have more capacity either because of higher pressure or they are larger
Buy a standard fibre instead of a standard steelie and the fibre will be heavier and more bulky. That ruins everyone's argument that they save weight
But to get a lighter cylinder you need a smaller then standard. A standard steelie is about 48ci, an equivalent 48ci fibre is lighter.
You get the same air capacity for the majority of time as 4500psi fills are not always available - most sites supply 3000psi and events may provide 4500psi
If you buy the cylinder for the weight saving then the fibre 48ci is the right cylinder
For more capacity you need to attend sites with higher pressure fills then you save weight and gain air
Without higher pressure fills to gain capacity you need the bigger cylinder, but then have not saved weight. When higher pressure fills are available then you get much more air per fill
Next brings us to why you do or do not need more air
If you can shoot all the paint you carry, or can last the length of a game then you do not need more air capacity. Fill your air when you fill your paint, and/or when you are eliminated, and between games
Sites have better air systems then when I started out, there are shorter queues at fill stations then there used to be - and if 4500psi and 3000psi fills are available the queues are like the toilets at clubs and pubs - no queue for the men's toilets / 3000psi, long queue for the ladies / 4500psi
(A tip for 4500psi users - when there is a 4500psi queue, especially at the start of the day, use 3000psi fill stations first. It spreads you all out and you can top up on 4500 or if game on is soon then you're ready quicker)
Now do you need weight savings and certain sizes - balance is more important
Your gun is heavy to you if it is not balanced to you. If the weight is the cylinder then that's irrelevant when shooting as the cylinder is your stock and is in your shoulder. If its not attached and you have a remote line then weight is irrelevant as you wear the cylinder
Balance and size are much more relevant and contribute to the ergonomics of your gun. Get these right and fine tune the position with a sliding rail asa mount and that is the real reason to buy a fibre cylinder - they come in a greater variety of sizes and shapes (big, small, short, fat etc)
A benefit often forgotten about the fibre is that they have curved bases, steelies have flat bases. You can naturally roll a fibre cylinder in your shoulder
This is irrelevant for many payers, but a big difference if the player is the type to duck in and out rolling the gun into place and for direction or carrying 'at the ready' and snapping on target to shoot
(That's the 'at the ready' position in a paintball sense, not the military position)