I have used to the ultimate and Gone through every experiment with Firestick...I can tell u
1. u can get decent experience of streaming from various app like Youtube, hotstar, Voot, alt balaji,Prime Videos,Netflix,Gaana,Arre,Dekho ,Tvf etc etc...
2. u can sideload whatever u want from high end Kodi to low end Ditto Tv. everything, Ok! Almost everything.
3. U will not get 4K though . maybe in future they will provide by changing some hardware.
4. A tiny portable devicethough truly not portable as u need a fixed power source with it.
5. u will get a voice remote.