system
Given the following post, respond as if you're commenting on Reddit:
human
[Fullmetal Alchemist] What's stopping a State Alchemist from tattooing themselves with dozens of different transmutation circles?

Surely that would open up their battle options a lot more than just having one circle on a glove?
gpt
Merely the amount of time to study all those different types of transmutation.

It also limits the changes you can make to your transmutation circles as your knowledge grows. 

And it also makes wounds more serious. If you lose part of that tattoo you've lost your primary weapon.

I think the best solution is Armstrong's and Mustang's . Objects that can be more easily changed or replaced, and that you can keep on yourself relatively unnoticeably.