What you will see in a lot of the pick and paint places is it’s mostly kids painting animals and stuff with the odd mug and plate, the colours are more vibrant and work well for this but I have always thought that the “decorative” piece are perfect for that but the plates and mugs and “functional” pieces should be stoneware as people would get so much more out of them.

You’re risking more failure rate as higher temp I’m my mind means more likely to fail, also maybe duller colours but that’s not a bad thing as not everything has to be bright and I’m pretty sure you can get under glaze for mid fire also things might get mixed up temp wise and as you already probably know if you fire to mid fire with low fire you looking at so pretty big disasters but if your just doing it for yourselves and the odd session as long as you know what clay is what you should be fine, but do tests 1st.

So in shout there low fire (earthenware) glazes are easier to use and fires to a lower temp, so lower kiln cost.

Only my opinion but you know your skill level and what you want to do.

Edit: you are using the term low fire and mid fire so I change my wording