Enter Moment's new 58mm telephoto lens. The company's made it proportionally larger than the older 60mm lens to match the larger sensor sizes of modern smartphones, which should, in turn, result in a much sharper image across the frame. All conversion lenses have a bit of distortion, though, so we'll be on the lookout for potential pitfalls like soft edges, weird halo effects and overall image sharpness.
Portraits
Setting aside the software portrait mode many devices employ these days, Moment's 58mm telephoto lens will bring you about two times closer to the subject and, as an added bonus, will give you a bit more bokeh without any software tricks. You might be thinking, "But my phone already has a telephoto lens," but here's the rub: Those cameras have smaller sensors, which means poor low-light performance and less bokeh in the background.
In practice, attaching Moment's telephoto lens to your main camera provides much higher-quality portraits than your phone's built-in telephoto lens can. They're sharp in the middle with no noticeable chromatic aberration (or color fringing) and bring you just a bit closer for that more-candid feel.

Now, let's talk about that software portrait mode. Dual-camera devices like the iPhone XS, Galaxy Note 9 and Galaxy S9+ use the secondary camera to calculate depth, which is then used to blur the background in their respective portrait modes. Problem is, Moment's telephoto lens will block the secondary camera, meaning you can't use it. However, the Pixel 3 and iPhone XR have portrait modes that only need one camera, and those can be used with the Moment Lens telephoto.
The combination of Moment's telephoto lens and software portrait mode on the Pixel is extremely good. I couldn't test it out on the iPhone XR yet, though, since the case is only available for pre-order right now.

As you can see, the background has an ample amount of bokeh, so much so that I would probably tune it down a bit after the fact. This combination of optical telephoto and software portrait mode provides some of the most pleasing portraits I've seen from a phone.
Landscapes
For photography newcomers, it may not be obvious that landscapes are often shot with telephoto lenses. If you're capturing natural splendor, more of the scene would be better, right? Not always: Sometimes you want to zoom beyond your immediate surroundings and focus the eye on that ridge out in the distance or a waterfall across the lake. Moment's 58mm is perfect for that.
But unlike portraiture, where you probably want the background to be out of focus, landscapes need to be sharp across the entire frame. This means that any distortion or softness at the edges will be easier to notice.