Welcome to the forum!
When we determined that we had to have a 2nd AC I went with the Dometic Penguin II low profile 13.5k unducted and no thermostat. The primary AC is a Dometic 15k. I decided on the Penguin II because of the lower profile and it just seemed to look nicer up front; the 15k just looked like a big box and the Penguin was more "stylized" for lack of a better term.
I don't know which brand yours came with but I would stick with whatever it is for the 2nd unit as well.
We like the unducted unit with the controls on the front because of simplicity I suppose. For us, having the unit controlled right there means we can dump cold air when we want without affecting anything else and make the bedroom "frigid" when we want to (we like to sleep cold - but NOT in the snow
).