All the smart TVs are the same tech as cell phones. They just have giant screens. Unfortunately, they are still designed as television and not designed as phones or tablets. So the UX is not as good.
I haven't gone with 4K displays yet although I am 4K ready. I have a 4K AVR and a UHD player. My computer can probably do it but there are some things I consider:
1. Display distance.
This is a common chart for size vs distance, but it is a general rule. I can tell the difference between 720p and 1080p on a 30" screen at ten feet, so the chart does not match up with me personally. My maximum viewing distance is around 10 feet. Placement of set is limited to one wall, where my other TV is situated, mostly due to sun traversal and heat paths in the house.
2. Due to the short distance, there is a maximum display size that I can use because a display that is too large ends up causing visible edge issues. Currently at 40", I presume a 55" is going to be around the maximum size I could use in that space. I am thinking that a 4K of larger size at greater distance would be most optimal.
3. Features and price. I have no desire to have a TV with a computer in it, at least a Linux computer like current CE 4K TV have, so that leaves only monitors. And while 4K monitors are competitively priced with 4K TVs, it is only to a certain screen size. This is where the cost savings of the CE TV takes over and the price is much lower than monitors. This is because the companies that make the included software in the smart TV pays out royalties to the TV manufacturer. This expected royalty calculation per unit is why 4K TVs are able to be lower in price. This business model also exists with computers (why your Dell has McAfee or whatever installed) or even in modern game consoles. The royalty earnings allow for a manufacturer to sell a device at or below cost because they will make up the losses with the royalties. Non-smart 4K displays, having no extra software installed, have none of these cost savings, which is apparent when you get to the larger screens.
4. Usefulness. There isn't anything that I have or know of that requires 4K. UHDs and anything else I can use will downscale to 1080p and at 40" the only difference I can see between 4K is that 4K downscaled has slightly sharp or bright edges due to image compression. By and large it is not really noticeable.
So I can't really see myself bothering with a 4K screen anytime soon unless there comes a situation where it is required for something.
