Did you have any specific questions about the Revvl?
Here's my opinion of my Revvl after five months of daily use. It marks my return to Android after my introduction with the Moto2. I came to this phone from the Nokia 925 and Microsoft 640.
The screen and camera are both fine, nothing particularly good or bad about either component. With a case on the phone, GPS doesn't work well. Bluetooth isn't stable and often requires a restart to get it to successfully pair with many devices (headsets, cars, portable speakers, etc.) Battery life is fair at best and with average use to text, read email and running a few apps, it will run about 15 hours. Bluetooth, when it's working is a huge battery hog (approaching 1/3 of the consumption observed). The fingerprint reader works well. The phone doesn't support NFC which means no Android Pay tap-to-pay.
T-Mobiles lack of transparency about Oreo ever being available for this device (manufactured by Alcatel for T-Mobile) is also frustrating and concerning and doesn't give me any hope that anything beyond Android 7.1 will ever be available for this device.
Based on the specifications provided by T-Mobile, the phone lacks 3G and 4G support on non-North American bands. Most notably lacking band 1 UMTS. This would mean that this phone simply will not work in Japan, South Korea and Singapore; and would provide a poor experience in most other countries where 2G is being depreciated (see https://support.t-mobile.com/thread/141048). It also does not support the 600 MHz and 700 MHz frequencies.