An unlimited plan can have a full-speed allowance or other fair-use conditions. Check the terms for the specific plan; there is no single speed or daily allowance for every SimFuse plan.
Before buying
Look for the full-speed allowance, any reduced speed, reset period and hotspot conditions. If a detail is not shown or is unclear, ask support to check it before you buy. Do not treat a missing value as a promise of unrestricted full-speed data.
If your connection slows
A fair-use threshold is one possible cause. Signal, congestion, device settings and VPNs can also affect speed. See "My connection is very slow".
Reduced-speed service may not be sufficient for every app or task. Usage reports can be delayed, so the app may not immediately show the activity that reached a threshold.
Hotspot traffic uses the same connection and can consume the plan's allowance where tethering is supported.