The Good: The Vivo X21's slim, thin design stands out, while its long battery life will easily last you a whole day. The camera is capable of taking pretty good pictures, too. The Bad: The iOS-like copycat design is horrible to use, and the phone's underscreen fingerprint sensor takes longer to unlock your phone than a physical sensor. The Bottom Line: The Vivo X21's cool underscreen fingerprint reader offers a glimpse into what a future phone can be, but it's not compelling enough to buy for the tech alone. The Vivo X21 may take inspiration from the iPhone X's operating system and screen notch, but it beat Apple's iPhone to one important thing: An underscreen fingerprint sensor.In fact, the Vivo X21 can claim distinction for being the world's first phone to sell with a fingerprint reader baked into the display, though other phones have since used it as well, including devices from Huawei, Xiaomi and another from Vivo itself.An in-screen (or underscreen) display is cutting-edge technology that's been rumored to come to iPhones and Samsung phones for well over a year. Putting the sensor on the display frees up space on the front and lets you unlock your phone without picking it up to use the reader on the back. Unfortunately, the particular sensor Vivo uses isn't as fast as a physical reader -- so don't buy the X21 just for that.Fetching a cool S$800 (which converts to about $600, \u00a3440 and AU$800), the X21 isn't cheap, but it is a pretty decent phone on its own, as long as you can put up with its copycat iOS skin and its iPhone X-ish looks. You should get the X21 if you're a fan of clean design, a large display, solid battery life and showy fingerprint tech that will stop your friends in their tracks, but skip it if you're looking for fast performance and tired of the recent slew of iPhone X copycats.The Vivo X21 isn't officially available in the UK, US or Australia right now, but there appear to be third party retailers that offer the phone for sale online in those markets. Just make sure it'll work with your local GSM bands.Vivo X21's underscreen fingerprint reader is slow, but battery life is greatPhone tech hasn't really changed much in recent years, with dual (or triple) rear cameras the last big game changer. Under-display fingerprint scanning has potential to free up more real estate on the phone, but based on my experience, it's a lot slower than the instant unlocking you get with a rear or home button scanner. That's because when you put your finger over the scanner, which is made by Synaptics, the screen has to light up your finger before it can scan it, and this takes some time. When your finger doesn't quite match up, you have to repeat the whole process, which is frustrating, especially given how instantaneous the "older" solution is. Perhaps Qualcomm's upcoming under-display ultrasonic scanner could be faster, but we'll see. For now, though, being an early adopter won't give you a speed advantage.