The Ran Zero is an amazing jacket, but it's very specialist with weight/bulk reduction being absolute. It's basically a really warm mid weight alpine jacket, but it's actually lighter than my ME Arete. It does that in the classic way of you can have it cheap, you can have it durable, you can have it light - pick any two. The 1000 fillpower is insanely high (it's the sort of thing you might find on PHD bags), plus an ultra light fabric, even by the standards of down jackets.
For a mid weight jacket around town, it's total overkill. Ran to very decent ones with a lower but very good specs. The Electron is a good example, and there are lots of other brands.
It's not a mid layer jacket. But Rab do the excellent Microlight (Which I probably would have got had it fitted me) or the Altus if you want synthetic. Lightweight, and fine as a mid layer if you need it, or as a jacket which you would use when you want something light to wear, rather than a fleece.That's how I use my Arete, and there are loads of similar jackets from TNF, Montane ME, Berghaus etc. You can get down or synthetic.
Frankly, I often use a cheaphish Decathlon synthetic jacket that I bought for £35 - works fine. Fleeces are ok, but they are not as efficient as an insulated jacket, and have no wind resistance, unlike this type of jacket.
If your using it as a mid layer, you don't need the fabric to be all that robust - that's what's the shell layer is for. I certainly don't use my down jackets when talking the dog - the Decathelon jacket as a top or mid layer, and probably a Barbour on top if it's cold/wet.
Go to Cotswold or Go outdoors and have a look at them, and try on the ones that look like they might work for you. The end of line and returns rail can be good value if your lucky, and black Friday is coming up, plus eBay.
Looking at Go Outdoors, they have the Microlight (probably the Old version) without hood for a £100. That's a good price, and worth going in for to try on.
Damn - double post.