Like SRAM XX1 and XO1, Race Face's new Narrow/Wide chainrings use a fat/thin tooth profile to aid chain retention. The idea is that this interface with the inner and outer link plates on the chain and stops the chain falling off when riding choppy terrain. The key difference between XX1 and Narrow/Wide is that the latter fits a regular 104 BCD crank. Which means you don't need a special SRAM crank or XX1 spider.
One of the reasons SRAM created the bespoke spider is to accommodate the smaller XX1 chainrings (these are available in 28-tooth for steep climbing), but Race Face offers a 30-tooth by offsetting the ring slightly inboard of the cranks uising thin alloy spacers [ed note: this spacing is machined into the chainring].
Like the company's standard Single rings, the Narrow/Wide rings are machined form aluminium plate with an 'I-Beam' cross section that reduces weight and adds stiffness. The anodising wore off after a couple of rides but I've had zero issue with wear on the teeth themselves. Retention is still as good today as it was when I fitted it two months ago - in fact, I've yet to drop a chain.
You may not get the 11 gears of the full XX1 system, but in terms of retention the Race Face is comparable to XX1, it's cheaper and , since it'll bolt straight on your chainset, there's no need to make massive changes to the rest of your drivechain.
For trail riding, Narrow/Wide rings and others like them look set to revolutionise chain retention because they offer one of the best features of XX1 but at a fraction of the cost. If you're going to buy a new single ring for your bike, make sure it's this one.