A lot of the time, if you go with something from a cheap store that only has cheap products, you may get a lower quality chemical that you need to use more of.
Now you're aware of what to watch out for when it comes to chemical drain cleaners.
For instance, if the cleaner can dissolve the pipes connected to the drain, then you need to know to flush the system out as much as possible after you try to use the chemical the first time or two.
Even if you're able to mix something according to what you read about it, make sure you're in a nicely ventilated area so that if anything happens, you can know that you're getting fresh air quickly.
That way, you will know that they have the right tools to be safe as they clean the area with a certain chemical.
The disadvantages of chemical drain cleaners will show you that while there are issues, cleaning chemicals can be worth working with.