You can go through the Amazon website any day before and buy a Fire TV Stick for $ 40, but that's just the 1080p version. Fire compatible with 4K usually costs $ 70. That is not the case today. Amazon Prime subscribers can now get $ 30 from 4K Fire TV.
The 4K Fire TV is a bit bigger than the 1080p Fire TV Stick, but it still hangs behind your TV. Run Fire OS, so you have access to Alexa and all the usual Amazon content. However, you are probably buying this because you want a 4K video. You can watch TV UHD and movies through applications such as Netflix and Amazon's Prime library.
At $ 40 million, the 4K Fire TV has the same price as the Fire TV Stick. Again, this discount is only available to Prime members and only for a limited time. How limited we do not know, but do not wait too long. There is no reason to get Fire TV Stick if you are a Prime subscriber.