I love the 4k Firestick and IPTV works amazing on it.
Done loads for friends etc.
I am sure it works great for you but for me the Z8 Pro is just different class.
£124 is quite pricey for a box but it really is a superior device.
All down to personal choice, but if the budget exists then the likes of the Z8 Pro/ Nvidia Shield are simply a class above.