As a quick reminder, metals can be recycled indefinitely. Plastic cannot, you always have to include some virgin material.
Also if you trade it in when it breaks, they only give you €50?
Plasticised PVC, which is where phthalates are used, is not suitable for structural applications like this.
Even something of equal weight like the legendary Surly Long-Haul Trucker is going to last longer and be more practical in every possible application. Maybe if you live somewhere costal and salt will corrode the steel or something it makes sense? I have a hard time believing this would fair better though.