Most mindfulness teachers advise clients not to multi-task, or at least to be reluctant to do that.
I also advise clients to minimise multi-tasking. I say this because if a client is at the stage of wanting me as a teacher/mentor/coach then trying to master multi-tasking and staying fully mindful is probably not helpful for them at this time. If they need to get things done, they are better just going fully into the flow and getting the outcomes they need, and going back to being more aware when the pressures are less. On the other hand, at some point multi-tasking can become like playing a team sport – keeping track of several things at once, being fully involved, getting great satisfaction from being so fully involved. This can be thought of as an advanced form of mindfulness, and the main difference is the lack of stress compared to ‘every day’ multitasking….
So, if you can multi-task without stress, why not? If there is stress present, reduce the task load at the first opportunity, and take steps to get your mindfulness practice to the next level then experiment again….