Even though the sketch is a great app, it needs to go further. Now it is just built only for MAC there is no other OS will not run the sketch. Photoshop is the widely used UI design app these days. Switching to sketch makes many issues. Sketch will not support PSD formats. I personally like Sketch a lot, but I have no idea how do I work with my clients. Most of my clients want PSD as output.
I am sure soon sketch will catch up its limitations. Sketch has some awesome features that other apps can dream of. We recommend to try and practise sketch. As Sketch is catching up fast, there are plenty of resources for sketch are already out.