Ignore the fact that portable air conditioner units may resemble “R2D2”, you need to make your decisions based on real facts some of which are presented here.
First thing you need to do is search the Internet for information and you will find that people voice similar concerns. The major concerns are those of price, energy consumption, noise levels and venting.
Keep in mind the amount of hours you will be using your portable air conditioner unit and then look at the Energy Efficiency Rating (or EER) or the units. Basically, the higher the EER rating the more energy efficient the unit will be. EER ratings of 8 for example, are at the low end of energy efficiency but these tend to be the older models. The average rating today appears to be around 12 which is good.