It will probably work in the short term, but the problems are
Crates like this are usually made from poor quality wood which soon rots.
To prevent rotting or insect damage in hot climates, the wood may have been treated with chemicals that harm plants.
The pieces of wood may be small, so the finished structure may look untidy because of all the joints.
The crates are usually made using nails that are designed so that they won't work loose when the crate is being used, and it is hard to remove them without damaging the wood.
In the UK, it would certainly be better to buy some timber like this which is intended to be used in permanent contact with soil outdoors and should last at least 5 to 10 years. That type of product might not be available where you live, of course.
Metal edging would be much more expensive than timber, and not really necessary unless you want it to last a very long time with no maintenance.