This is an excellent point. I've had both the Garmin Mk1 and the Shearwater Teric on my wrist (although not at the same time!) and from my perspective these are two very very different devices created out of two very different companies. It's temping to compare them because of the shape, but they really target two different types of consumers.
They are both wrist-watch form factor devices with support for sport and technical diving. Both can be worn as a daily time piece. Perhaps the easiest way to differentiate them is by considering their brands. The Garmin Descent Mk1 is from a company that is well respected for their powerful multi-activity sports watches and GPS devices. The Mk1 is based on Garmins' top of the line Fenix 5x smartwatch that includes GPS and a heart monitor along with additional support for SCUBA diving. The Shearwater Teric is from a company that is well respected by experienced divers for their dive computers. The Teric is based on an enhanced version of the powerful diving feature set of Shearwaters' top of the line Perdix AI with a new wrist-watch sized form factor that focuses on diving related features. The diving functionality of the Mk1 is new to Garmin and the compact form factor of the Teric is new to Shearwater.