Yes, 4.6V isn't really enough, and ROK are pretty brutal really.
A Bosch or a Makita would work well with only 4.6V, but really you need about 9.6V minimum, or 12V or 14.4V for better results.
The LIDL Parkside tool manuals can be downloaded on
http://www.kompernass.com
You have to choose the language and then the brand Parkside, then look for the manual. The manual might list the torque.. for example, a 14.4 Makita screwgun has a torque of about 36Nm.. this is quite good.. a 6 x 100mm screw could easily be screwed into softwoods using that.
This screwgun
[broken link removed]
on special offer, 70 UK pounds, down from 110 pounds, with three batteries, would be very good and is a professional tool, used everyday all day by professionals.. (torque = 30Nm, should be loads for light-ish work) ... you might not need that quality of screwgun, but it would likely last decades if looked after.
I think the Parkside tools are good, and that screwgun for 20 Euro does look pretty good, and it should handle assembling flatpacks.
It's not recommended to use power tools to assemble flatpacks. If you had the Makita you can specify the maximum power the screwgun should use, so they can be used safely as the power can be turned right down, and you finish tightening each screw by hand.. no risk of damaging the cabinets. The LIDL Parkside one is incredibly cheap, at 19.99, for a 13.6 Li-Ion screwgun, with 26 bits. Li-Ion is the best battery technology available, within reason, maybe NASA have better batteries for spaceships or something but Li-Ion is very good. The LIDL one also has a 'clutch' which allows you to specify a lower power setting to avoid damaging workpieces.
Crap batteries will discharge over time by themselves... this can be annoying for DIY use, as you have to remember to charge up before use.
Cheers so
Joe