At this time, they have to be purchased in a set of three or six. I hope the below information is helpful.
Why are Pods only offered in sets of three or six?
Pods are designed to work in sets to help ensure that WiFi coverage is extended to every corner of your home. Although some homes may only have one area with poor WiFi coverage (also known as a "dead spot"), simply installing a Pod in that area will most likely not address your coverage issues.
Your first Pod should be placed in a room halfway between your Gateway and an area without coverage. If you have additional areas of your home that need coverage, your remaining Pods should be plugged into outlets halfway between your Gateway and those areas.
Do I have to use all of the Pods that come in the set?
No. Simply plug in the Pods that you want to use, and when activating your Pods via the xFi mobile app, select All Pods Ready to Go. On the following screen, select Not Using All Pods.
After activation, the unused Pods will show as Offline in xFi. See below for instructions on how to remove your unused Pods from xFi.