Does the 'Recipients' metric in Statistics count unique users or devices?

The Recipients metric counts devices, not unique users (UserIDs). The metrics glossary defines it as "devices with enabled push notification alerts". A device is counted when it is able to display the message. If one person has several devices, each device is counted separately.

Where you can see unique users instead of devices

• Unique users and Total reach in Customer Journey statistics, and the Unique Users column in the campaign statistics CSV export (Export statistics in the Campaigns list).
• MAU and DAU on the Project overview page, which are user-based rather than device-based.
• Unique users on the segment size card (see below).

About the "Include all of a user's devices" segment option

This option controls device fan-out, not per-user deduplication:

• Enabled — if any device of a user matches the condition, all of that user's devices are included.
• Disabled — only the devices that actually match the condition are included.

Turning it off therefore does not guarantee one message per user: a user with two matching devices still receives two messages.

Segment size

The segment size card reports both figures — Unique users (distinct users in the segment) and Devices broken down by channel (mobile, web, email, SMS, WhatsApp, LINE, Viber, Kakao, Telegram) — so you can compare user reach with device reach directly. Both are a snapshot: the final number of subscribers can still change when you launch the campaign, because device availability and subscription status change in the meantime. See Calculate segment size.