13 is a good “on call”/travel size. It’s not big enough to do serious work on but in a pinch it’s definitely big enough to get something done. It’s more comfortable on a flight, you can toss it a fairly small bag and take it with you. It’s lighter but can still manage a reasonable size keyboard. And when I get to my house or my job I’m plugging into external mouse and keyboard anyway.
It’s not for everyone but my 13-in motherboard died about 2 months ago and I am definitely in the market. Now if I can just actually buy one of these we’ll see.