It tries to both be 'good like a controller' and 'good like a kb/m replacement' and it's really neither of those.
Tbh it really is a damn good controller for replacing a keyboard and mouse, due it's sheer control customization and personalization.
Imo you should only get the Steam controller if you're fine with having to map the controls to it and configuring / tinkering and such. Also if you have games that don't have controller support, the Steam controller can have it's inputs mapped to keyboard / mouse inputs
I mainly play older games / casual games which is perfect for the controller. Anything more and the controller just isn't good for it. The controller is made for casual / calm games or racing games (using the gyro as a steering wheel is really damn fun and 50x better than brown townog stick)
Oh and if needed the controller can also emulate Xbox 360 inputs as well