That's a real good question and depends on who you talk to (and what they are selling).
Here's a quick run down:
- Plastic unless protected out in the sun and weather breaks down - we have all seen plastic that has been outside for some time and it becomes hard and brittle
- Plastic in a fire will ignite or in high heat will deform
- Plastic is made from chemicals that leach out over time and may end up in your water tank
- Plastic needs to be manufatured thicker for strength so will cut down on water into the gutters or cause more water 'sheeting' (run off)
Aluminium and Steel don't have these problems and are 'cleaner' materials to use.
People ask us why we don't use plastic? As we are independant we can use or buy what ever material we like - but when it comes down to it at the end of the day we need to provide a warranty and stand behind the product we use, as we don't want any problems (just like you don't) we only use Aluminium and Steel mesh.