What is the opinion of Reddit about the
Sabaj Audio PHA2 Portable Headphone Amplifier Silver Color?

Sabaj Audio PHA2 $59.

Can we ask what part of Europe, and why RCA connectors? Is that 3.5mm to RCA from the Computer to the Headphone Amp? But standard 3.5mm to the headphones?

Using Amazon-UK, there are quite a few moderately priced Headphone Amps available.

https://www.amazon.co.uk/s?k=Headphone+Amplifier&ref=nb_sb_noss_2

I don’t know your budget, but something like this might do the job –

https://www.amazon.co.uk/Sabaj-Audio-Portable-Headphone-Amplifier-silver/dp/B01EUFICO6/