Whether one selects to purchase a de-curler or make their own is a personal choice. Some prefer to save their money, and enjoy the process and challenge of building one and developing a technique to make it work. Others would prefer not to spend time that way and buy a high quality product.
A do-it-yourself decurler costs less than $20 and a bit of time. To purchase one costs more than 10 times this amount. (The hammer analogy given in a previous post is not quite fair. A hammer does not cost $200). In my case, I built one with the idea that if it did not flatten well and/or was awkward to use, I would purchase one. The one I built works fine. It may not be as easy to use as the commercial version, but just requires a bit more care in the process.
Either way, (build or buy) you can have a de-curler that works effectively and efficiently, and you can end up with a flat sheet of paper with no marks or blemishes from the de-curling process. No-one will be able to distinguish how it was flattened.