Firestick IPTV is best understood as three separate pieces: the Fire TV device, the IPTV player app and the authorised subscription or playlist you load into that player. Keeping those parts separate makes setup easier and avoids many common mistakes.
What to check first
Before buying any service, check the account format, app compatibility, EPG support, cancellation terms and whether the content is properly licensed for your use. A low monthly price is not useful if your favourite channels are unreliable or your device cannot run the recommended player.
Practical Firestick advice
For most UK households, Firestick 4K or 4K Max gives the smoothest experience because it handles larger playlists and modern player interfaces better than older sticks.
Use IPTV apps and playlists only with sources you are authorised to access. A player app does not provide channels by itself.