Rab says that in a size large the jacket weighs 27.7oz (785g) and has 9.7oz (275g) of 800 fill down. Baffled or box-wall construction, like a sleeping bag, makes it warmer than a jacket that's sewn through but otherwise similar. The North Face Nuptse jacket is a classic example of sewn-through construction. Rab's Neutrino Endurance Jacket has less down and sewn-through construction. This makes it a little lighter and cheaper, but also a little less warm. Other than that the features on the Plus and Endurance jackets are almost identical.
Being a skinny guy with long arms, I've come to appreciate the way that Rab cuts their outerwear. This jacket has a nice long cut in the torso, and it's even a little longer in back. It keeps my hips nice and toasty and even when reaching there are no nasty drafts. I didn't think much of this feature at first but I've come to believe that my core is kept a lot warmer by it. The hood works well over a helmet but also adjusts nicely for when you're not wearing a helmet.
The zipper is a two way separating zipper. This means that the zipper has two sliders and when you put the jacket on and zip it up all the way, you can reach down and zip the lower slider up allowing the jacket to open up at the bottom. The big advantage here is when belaying. The jacket can be down around your hips keeping you warm and not interfering with your belay device at all. This is a small detail but makes a big difference in actual climbing applications. I wouldn't buy a big belay jacket without this feature.
There isn't anything I really don't like about the Neutrino Plus, but there are a few features that I find unnecessary. At the bottom of the main zipper is a small snap. I imagine this is for keeping the jacket snug around your hips when you've opened the zipper to use a belay device. I have yet to find it particularly useful.
There's also a velcro flap inside the jacket that lets you roll the hood into a collar. I cut this off. I find that if I don't want the hood up (usually for better hearing) I can just zip the jacket up all the way and the hood nestles the back of my neck nicely.
Rab clearly clearly designed and built this jacket for use in pretty cold temperatures, well below freezing kind of temperatures. In those types of conditions one is probably not going to encounter much liquid water and certainly not liquid precipitation or even wet snow. This makes the Aquaguard waterproof zippers on the handwarmer pockets seem like overkill. I would prefer a regular zipper as the Aquaguard zipper is a little stiff to open and close.
Neutrino Plus in the included stuff sack. The jacket could easily be compressed to about half this size.
MARCH 2014 UPDATE. It looks like Rab no longer sells the Neutrino Plus. Their website only shows the Neutrino Endurance.
JUNE 2016 UPDATE. I've now used this jacket for 5 trips to the Alaska Range, including 3 trips up Denali's West Buttress. I still wish it had the DAS Parka - style big drop-in mesh pockets, but otherwise I'm really happy with it. I have yet to be cold with this thing on.