Smartthings is an extremely versatile, powerful system. But they have yet to solve the stability issues. They are definitely aware of the problem, and have said they are making reliability their top corporate priority. But they aren’t there yet. There was an outage of several hours just this last week.
Since last November, I personally have yet to go 10 days without an impactful SmartThings failure. So I have moved everything critical off of it that doesn’t have an immediately available Plan B.
If you use the Fibaro relays, they themselves are very reliable. And even if the smartthings hub goes down, The switches will still work manually.
However, your tablet on the wall will not work with smart things if your Internet, or even just your smartthings cloud account, is not available.
In fact, if your smartthings cloud account is not available, even the official mobile app on your phone will not be able to talk to your hub. Technically they could, it’s just not how SmartThings was designed. It’s a cloud-based architecture, still, although they have added a small amount of local processing for some lighting features.
So you do you need to design for a Plan B for pretty much everything. Certainly it doesn’t compare to the reliability of a control 4 system, but obviously those are many times more expensive.