In reply to Jonnylowit:
Over the years I have bought many climbing / mountaineering items of clothing. Some have been great purchases and some not so ( although I've often thought they were great at the time of purchase or because I did not know any of the alternatives - plenty of conscious incompetence in my case! ) Also manufacturers / brands change their designs so sometimes one brand has just the features I'm looking for but a year later the design changes and a different brand has the features.
So, eventually learning from watching and listening to others, I've changed the way I approach a purchase. Reviews and what other people suggest is usually worth listening to ( I think Dan's reviews are excellent) but IMO the most important part of the decision making process is examining exactly what features you personally want from a product. This has to bear in mind main intended current and future usage, most common conditions in the areas you will use it, how the clothing fits into your current clothing options, what feels comfortable and right for you ( we all operate at different paces / temperatures ), environmental factors may play a more or less important role for you personally, price and availability. Sometimes I'll even rank the features into 'essential' or 'desirable'.
You have outlined summer use as a belay jacket in Scotland walking and scrambling, will you also use it when rock climbing ? Assuming you mean rock climbing too I would look for as close a match to the following features as possible:
Synthetic fill - quick to dry, reasonably drizzle proof, most efficient insulating and environmentally friendly I can afford
Strong wind resistance
Hood that goes over helmet ( adjustable )
Pockets accessible when wearing a rucksack / harness and can act as hand warmers
Lightweight 40 - 60 gram fill ( for an active layer more towards 40 but for a jacket to put on when stopped or for the evening more towards 60 )
Cinching cords for a more snug fit when required
Sized to go over my normal active layer ( possibly even over my summer weight hardshell jacket )
Ideally sleeves that can be pushed up the arms
Full length zip for greater versatility
Compact and ability to pack into its own pocket with a strong loop attachment for putting onto a harness.
Sometimes price may trump all; Decathlon often have cheaper and reasonable alternatives with some of the key features. Have fun with the decision making...