"A cheap international calling card that happens to include a little mobile data."
The '4GB of high-speed 5G/4G LTE data' means you get T-Mobile's top speeds for a very short time. It is enough for light browsing, email, and maps, but not for regular video streaming or large app updates away from Wi-Fi.
This plan is for users whose primary need is making international calls to the specific countries included. It's a logical fit for those who use Wi-Fi for almost all data consumption or need a low-cost line for a backup device.
Anyone who streams media, uses social media apps regularly, or relies on a stable data connection for work should avoid this. The 4GB data cap is too restrictive for an average smartphone user in the current market.