[wrxtasy]

Are the 'option e' boxes even worth buying, or would a RPi3 be better than them?
Are all cheap, sub €50 ('option e' in that post) S905/S905x boxes "the same" in terms of performance (ignore build quality etc) or are there certain ones that should be avoided and others that are good?
Is an S905 better/worse than an S905x, or are they as good as each other in practice?

The RPi3 is relatively ancient Hardware in this 4K era. It is both slower and has Hardware decode and Ethernet limitations vs the AMLogic S8xx/S9xx Chipsets. It does do 1080p 3D however which AMLogic cannot.

Even my 3 year old AMLogic S805 would beat it in the performance stakes as a media player these days now is has a decent Kernel and bug busted LibreELEC Kodi Krypton running on it.

Have a look here if your want some raw performance numbers RPi3 vs AML S905(x)

S905 vs S905X differences:
AML S905 = 99% of devices have Gigabit Ethernet (still check carefully)
AML S905X = slower 100M Ethernet only & can handle HDR. Can decode 4K VP9 as well for what minor VP9 content there is. Good luck finding properly encoded 4K HDR content with correct HDR Metadata outside of Android TV only - HDR Netflix and HDR Amazon video streaming.

Honestly apart from the known branded WeTek's, ODROID, Vero4K, MINIX etc. I cannot name you a box to buy with any certainty. Beelink seem to be at least a bit consistent.
Internal hardware on the cheap brands varies slightly, pretty often.
Its a bit of a lottery what will actually be delivered. Avoid the MXQ Pro 4K - there have been deceptive sellers shipping so called AMLogic devices that turn out to be cheap $15 Rockchip rubbish.

It you need WiFi you have to be very careful as new WiFi Chipsets in cheap AMLogic do not have Linux drivers available.

Head over to the Budget AMLogic S905/S905X/S912 Media Player Options thread to see what LibreELEC Kodi users are buying and for further discussion options.