Get one where the fan cycles off and on with the compressor or it will run constantly. Fans are usually loud and not energy efficient. Cost more, but well worth it.
Some manufacturers will say no pan to drain, but there might be an area where water collects at the bottom of the unit in the back that must be drained for it to work. QVC's Delonghis are like that. This is a real pain because the units are heavy. I had to disconnect the unit from the window to do it.
Don't spend extra money for one with a humidifier included. AC's are very similar to humidifiers removing moisture from the air. My experience has been the humidifier just turns on the AC throwing out cold air. There is no humidistat inside where you can set the humidity to a certain level. Spend the money on a real humidifier.
Is their living room open where the AC might end up cooling other rooms? In other words, if connected to the dining room by a doorway, it would be cooling that too. Make sure to get the right size. I found you need a larger size than window AC's for the same square footage or it won't cool well.
Make sure the connection will fit their window. QVC's Delonghi I purchased last year did not fit my standard 29 inch window.
Look online to find a model to your liking. Look at reviews. There might be a demonstration on Youtube.
But, suggest you buy one locally. Ask for demonstration. Make a list of questions before you go.