Launched in the year 2021, the 65HK5600 is a 65" 4K TV from Hitachi. It comes with a 10-bit IPS panel. The maximum resolution it can achieve is 3840 x 2160 @ 60 Hz with a pixel density of 68 ppi.
Picture Quality
After screen size and resolution, the very next feature of a display that defines picture quality is Color Gamut.
Hitachi did not provide a color gamut rating for this TV. So we have to take a guess.
Now, since the TV features a 65 inch screen, it won't come with a cheap panel, so here we can assume its equivalent sRGB coverage to be 90-100% or above. Undoubtedly The color accuracy on this TV should be Lifelike! Meaning it is capable of producing accurate colors.
Understanding the Color Gamut Specification
Color gamut specification of a display is a measure of the range of colors that the TV can display.
What this means is, this specification indicates the ability of a TV to produce accurate colors. A TV with low gamut coverage will miss out on some colors (such as deep red), so the image produced will look "washed out" in colors.
Different manufacturers use different units to specify color gamut. Viz — sRGB, NTSC, DCI P3 to name a few.
But you don't need to worry about that, below is a chart that you can use to choose a TV with good color accuracy.
Now, after color gamut, you should look at the static contrast specification as it impacts the picture quality substantially.
The importance of static contrast ratio
There are 2 types of contrast specifications for a TV. Static and Dynamic. We are interested in static contrast ratio as dynamic doesn't matter much.
This tells the intensity of black levels. That is, a TV with static contrast ratio less than 1000:1 will produce black images something like this:

Note that, such TVs are also prone backlight bleeds that will impact your experience — as shown below.

Also, a TV with high constrast ratio allows you to see more details. So, resolution and static contrast ratio go hand in hand in a sense.
If given a choice, always prefer a FHD TV with high contrast ratio over a 4K TV with low contrast ratio.
This TV comes with a static contrast ratio of 8000:1., enough to produce deep blacks. The panel comes with local dimming backlight which is a plus.
HLG (Hybrid Log Gamma), HDR and HDR10 are also supported on this TV.
Coming to brightness, it can go as bright as 250 nits. The backlight used on the panel is Direct LED.
Gaming Performance
If you are not interested in gaming, you can safely ignore these specs. But if you are also planning to use the TV for gaming or use it as a PC monitor, you should take a TV that features the lowest input lag and response time.
Unfortunately, we cannot find the input lag specification for this unit. But as this is not a cheap TV, we can expect an input lag of less than 20ms.
Understanding Input lag and response time
This lag is the amount of time at which your inputs changes the content of your display. For casual Non-FPS games, input lag doesn't matter much.
For best of both worlds, get a TV that features an input lag and response time of < 20ms.
Dimensions and Ergonomics
The width of this TV is 57.2 inches while its height is 34.84 inches. Speaking of thickness, it is just 2.83 inches thick.
Overall the TV weighs approximately 20.69 Kgs including its stand. Without stand, it weighs 18.19 kgs. So plan your space accordingly.
Now, coming to ergonomics — a VESA mount with interface size of 400 x 200 mm is provided for wall-mounting. There is no Swivel, Tilt or Pivot feature support on this TV.
Hardware and Audio
The core of Hitachi 65HK5600 is powered by a 4-Core CPU. However, Hitachi didn't provide any specification on the total RAM on the TV's specsheet.
The UI on this TV is powered by Android 10 Operating System.
For display connectivity, there are three HDMI 2.0 (ARC; CEC) ports and one AV Composite In (Video + L/R) port on this TV.
For connecting USB devices, you will have two USB 2.0 ports. Other connectivity ports include — 1x Satellite In (Main — F-type female), 1x AV Component In (YPbPr + L/R) (via PC input), 1x Antenna (RF) (female), 1x CI+ 1.4 and 1x Ethernet RJ45.
For connecting to this TV wirelessly, you will have — Wi-Fi (5Ghz + 2.5Ghz), Wifi-Direct, Bluetooth and DLNA.
Coming to audio, it is packaged with 2 x 12W speakers.
In terms of power usage, on average, it uses about 174.4 Watts. On standby, it uses 0.5 Watts.
For powering this unit, you will require an 220 V - 240 V/50 Hz - 60 Hz outlet.