The plug-ins are quite large, you would not want to use them where they could be easily jostled about as when the wax melts it can go everywhere... just ask how I know this! Along with the two plug-in, I choose 6 different scents. The lady from Scentsy indicated that each scent should last about a week depending on how long and often you turn it on.
The cons: I have had the plug-ins about a month now and the smelly wax or Scentsy bar does not last that long. I would say on average 3 days if you are running the plug-in. The one in my office does seem to last longer, but; the room is smaller and I close the door at night. The plug-in in the kitchen does not seem to be doing much of anything. Granted, the room is large, open and the plug-ins are designed for smaller areas. But even when we are in the kitchen, I cannot smell it.
I would not purchase this product again. I love the concept and not having open flames, especially with children, pets, or someone forgetful. Overall, the price is high and I am disappointed in the product.
Disclaimer: Scentsy has no clue who I am... this is strictly my opinion.