WiFi is "free" in that you don't have to have a mobile data plan. It is not "free" in that you typically are paying for whatever service the WiFi is routed through.
The person getting the device should be able to use it as a WiFi device. However - I would HIGHLY suggest signing out of your Google account before giving it to them so they don't have access to your Google account. This also ensures they can sign back into it if they need to reset it.
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