The jacket tested (not the one linked by northcountryboy) has a RET score of 12 according to the Decathlon website. Without going into too much detail RET is an iso accredited way of measuring breathability. A RET 12 rating is ok, it’s on par with what you would expect from most outdoor and cycle brands non-branded membrane waterproof jackets. It’s not as good as any of the branded membranes (Gore, NeoShell, etc) though.
What is weird though is the relatively low hydrostatic head rating of 5,000mm. I say low, what I mean is in comparison to stated HH’s from other brands. Most ‘sporty’ waterproofs will have a HH of 10,000mm and over, although if I remember right 1,500mm of HH will be waterproof in rain. The higher HH in waterproof clothing is to make sure in high wind, high rain, higher pressure (e.g. when under a pack) that the fabric doesn’t get overwhelmed. The 5,000mm HH is weird in that you would normally expect a better RET rating from a fabric with only 5,000mm HH.