It can be used in a very wide spectrum of environments and has a high speed of access when running tests against these environments.
The environments are really easy to configure and the UI is very friendly.
Another great feature is the monitoring of test executions in real-time as well as the ability to perform actions on a testable web page.
It also has video recording and full logging, which are great and helpful functionalities.
Room for Improvement:
I think that I found maybe only a few gaps which I don't think are very important. These are more like improvements which need to be added.
It would be very good to see a short example of the code that needs to pass into Driver capabilities, something like auto-generation of this block.
Also, it's not obvious where to look for the API key. It would be very nice to have a button on the top navigation menu.
No issue with deployment.
No issue with scalability.
My general overall impression of Sauce Labs is very positive. I use Sauce Labs and recommend it to every engineer.