The fundamental difference between a free zone and a bonded warehouse is this: a free zone is a geographic area where production can be carried out; a bonded warehouse is a customs procedure where only storage and handling take place.
Both allow goods to wait duty-free; but unless your need is production, a bonded warehouse is almost always more practical and cheaper.
One question decides it
Are you going to carry out an operation that changes the nature of the goods? If the answer is no, a bonded warehouse is enough.
If the answer is yes, the warehousing procedure does not permit it anyway; a free zone or inward processing has to be considered.
Set-up and operating burden
Operating in a free zone involves company formation, licensing and a lease; fixed costs arise.
In a warehouse you buy a service: you sign a contract, leave the goods and pay for what you use.
Geographic flexibility
Free zones are at specific locations and the goods have to be moved there. Bonded warehouses are far more widely spread, close to ports, rolling mills and border gates.
That distribution makes a difference when you factor in transport cost.
What they have in common
In both, the goods are treated as not having entered free circulation in Türkiye and import duties do not arise. Duty comes into play when the goods enter the domestic market.
So the two are not competitors but different structures answering different needs.