I've had one pot dry out, but the key is to make sure the pot stays sealed. If it doesn't, usually this means there's some dried paint to scrape out of the lid, no big deal. Also, when shaking the pot, put your thumb on top of the lid. I also added a shaker (piece of sprue) and will add thinner and hobby paint (from another company's eye dropper paint) to the pot to keep it filled. (I buy paint on sale, even if one or two colors overlap what I have.)
Colored primers are sold in larger containers and some have caps. Won't dry out, and you can paint from the cap after shaking the paint. Personally, I prefer caps and pots over eye droppers because I'm assembly-line painting 20+ miniatures to advanced tabletop, and don't need mixing or subtle wet palette effects. Also, pots and caps are *much* more convenient for touch-up.
EDIT: If you have a 3D printer, you can print a Citadel paint funnel.
https://www.thingiverse.com/search?q=Citadel+paint+funnel&type=things&sort=relevant
Also, someone's selling a dropper top adapter, so you don't have to transfer paint. :
https://www.drtabletop.com/shop