Hmmmmm… I have a Montane Featherlite, but am loathed to use it most of the time – except in emergencies when I get caught out by unexpected bad weather. For this use it appears to be just about perfect – as you can stuff it away in its scrotum sack and just forget about it ’till you really need it…. but I wouldn’t want to use it as my primary rain jacket – it’s just waaaaaay waaaaaay tooo thin and tearable. I’m sure it’d fall to bits pretty quick if I used it all the time. A single layer of flimsy pertex is not very waterproof, breathable or warm either*.
I use a Ground Effect ‘Flashgordon’, which is great for right now in wintery rainy Tasmania, but I think you’re probably looking for a lightweight UK summer jacket, Hmmmm…? For this use the Flashgordon would be simply too heavy (and fairly bulky too).
Good luck with your quest!
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*NB I am using the basic Montane Featherlite – not the CRC H20 version as highlighted by one poster – dunno what that one is like, could be ok I suppose?