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Folding-smartphone releases from Samsung and Microsoft show the devices starting to carve out a niche as the equivalent of luxury cars. Still up in the air is whether these phones and their successors can propel the category from novel curiosity into the mainstream.

Why it matters: With the smartphone market slowing, manufacturers have an incentive to bet on new concepts. For now, though, foldable technology comes at a high cost with some key drawbacks cutting into the benefits of packing more screen into a smaller phone.

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Driving the news:

• Samsung on Tuesday debuted the Galaxy Z Fold 2, a 5G-capable successor to last year's high-end model. It adds a larger front cover screen and better camera, among other improvements.
• Microsoft's Android-based Surface Duo uses two screens rather than a single foldable display, and is set to be available on Sept. 10, starting at $1,399.
• Motorola, LG and others have also dabbled in this market, with more devices expected soon. LG has offered hints of "Wing," a phone whose second display swings out from the main one.

Catch up quick: True foldables, like the Samsung Fold, open up to a single seamless screen. The two-screen approach used by the Surface Duo leaves a gap between the two sides.

Between the lines: Samsung is positioning the Fold 2 like a luxury good, complete with white-glove service and a series of perks. Microsoft is focusing its pitch on productivity, showing all the different ways Surface Duo can help get work done.

The big picture: Neither the Fold 2 nor the Surface Duo is destined to be a huge seller. The key question is whether such devices remain niche products, like 3D TV, or the start of something big. What makes that tough to answer is that both flops and eventual mainstream hits tend to start as high-end products aimed at enthusiasts.

• With hits, the costs come down, driving demand, which further lowers cost. With flops, the interest doesn't scale, costs remain high and the technology tends to fade away.

What's hot:

• Multitasking is a lot easier on larger or split screens.
• Foldable devices look cool and stand out from traditional single-screen smartphones, which are often indistinguishable from one another at a glance.

What's not:

• High prices. Samsung's new Galaxy Z Fold 2 costs nearly $2,000, while Microsoft's Surface Duo starts at almost $1,400, making them as expensive as two high-end phones.
• Few apps are optimized specifically for the Microsoft or Samsung devices.
• Devices can be fragile, expensive to repair and are typically not water- and dust-proof .

Flashback: Foldable displays have been a long-time coming.

• LG and Samsung have been exploring the underlying technology for a decade, and both companies experimented with flexible screen smartphones back in 2013. Although they allowed the phone makers to add a bit of a curve to the devices, they offered little new functionality.

The bottom line: If money is no object, both the Surface Duo and Fold 2 will help your phone stand out from the pack. But since most of us aren't traveling in packs these days, the devices have to prove they can do more than just look cool.