If you’re worried about the amount of Minoxidil, what you can do as a simple solution is just use the serum very sparingly. I simply tap the end of the dropper on my scalp, without squeezing the dropper, releasing a tiny amount of the serum. This is all you really need. And it’s also a very good way to apply the serum because it means the serum stays in the epidermis (where it’s effective) rather than absorbing into the bloodstream.
If you’re concerned about the amount of Minoxidil I’d recommend only using the serum once per day, directly before using the Dermaroller and only using a very small amount by tapping the dropper rather than squeezing it.
Some people use 5% minoxidil but they squeeze a huge amount onto their scalps each time. If you think about it, if you use half as much serum as they do you are adding exactly the same amount of Minoxidil to your scalp, except you are only applying it to your epidermis, rather than applying a huge volume, which will cause a lot of the serum to absorb through the epidermis where it has little to no benefit.
Alternatively, you can send the item back and I can dispatch a lower strength for you. That is not a problem at all. However, I think you’ll be fine with the 10% providing you’re careful and you bear in mind that you are in control of how much you apply.