manufacturer is TANIX.
https://www.tanix-box.com/

tx3 (mini and max) is a very popular model since 2017; uses amlogic S905W chipset - a rather low end but functional one.

tx6 is a newer one with allwinner chipset; specs good.

BUT... specs on paper is not everything.. a lot depends on firmware and what u r looking for.

Tanix has tx2, tx3, tx5, tx6, tx9... many variations for all of them.

i do not know for sure but i think tx6 comes rooted, no option to unroot, u need someone/procedure to help u - please search n read.

unrooting is required to run astro go and unifi playtv... if u do not use them, that's irrelevant.

b4 u buy, list yr requirements to the seller and ask for confirmation, e.g...

.. ram + storage?
.. android version... 8.1, 9?
.. firmware version?
.. Alice UI?
.. option to close root?
.. can run astrogo, playtv.. other apps?
.. Bluetooth?
.. price?

there are like a hundred boxes out there.

price rm10x... 50x... 1xxx... 2xxx...

it depends what u want to it to do.

if u describe what u want it do, i can suggest a bit better... things like...

.. what stuff u want to watch online?
.. what broadband speed u have?
.. want to run astro go, unifi playtv?
.. using home theater? 5.1, 7.1?
.. doing much local playback.. i.e. yr own files... how big, what type...?
.. want netflix hd/4k or yr tv already have it?
.. have some exp with android apps procurement, installation, updates... with phone or tablet?