Warning - long meandering post to get to a point. I’m VERY new to ST in general, but this is solely my experience:
I’ve had SimpliSafe in my home for 3 years now. I have no major complaints, but it gets a mixed bag on these forums, so it’s probably not for everyone.
I started the smart home journey with Wemo + Echo. Hate it. I used 3 Wemo dimmers to “zone” my living room lighting. When I ask the Echo to turn on the living room lights group, the latency was sometimes up to 20 seconds for all three zones to turn on, with the occasional zone failing to respond entirely. My 60Mb ISP connection is pretty solid, so I’m not sure what the issue is there.
The master bedroom and kitchen were next. Found a Lutron Caseta starter kit on clearance. These do NOT work for everyone’s switch/dimmer use case. However, if it DOES fit your use case, I highly recommend the product. There are polarizing opinions on the styling of the switches, but I happen to like them. Even though Echo or ST need to communicate via the cloud through the Lutron hub, latency is almost never more than 1 second for me, I have never had a failed command, and the compatibility with disparate products is unbelievable.
Enter my first use case where Lutron wasn’t feasible. In the master bedroom, there is a tiny “hallway” of sorts leading to the master bath, with a closet on either side. The smaller of the closets (mine, because wife) has a light, but due to the size of the closet, the switch for that light was actually on the other side of the wall, in the master bath. I always found this annoying to reach around and feel for the switch, turning on/off the bathroom lights and fan in the process. Not to mention my wife getting ticked because I’m barging in on her bathroom visits every time I need something from my closet. Because of this, I decided to try a Z-Wave sensor. This is where SmartThings came into my life - because I wanted to turn on a closet light while my wife was on the toilet.
One cheap Z-Wave sensor, a cheap used ST hub, and a not so cheap Lutron switch later, I had about 40% reliability automagically turning my closet light on and off. Why? My router and hub are stuffed in a closet on one end of the house, and this closet is on the other. The Lutron was rock solid in all my test commands from the app, but the sensor wasn’t reliably reporting its status to ST. I had a distance issue.
I ended up moving my Lutron switch to another room where it better fit the use case, and replaced the closet switch with a Jasco/GE Z-Wave switch. I then added another sensor and switch to my wife’s closet. Once the Z-Wave network had a couple of good mains-powered devices, reliability was 100%. Latency was rarely more than 1 second, and at most 2 seconds, but reduced to 1 second or less once I added some fan controllers elsewhere in the house.
The latest phase was integrating SimpliSafe with ST. I had to use some custom code provided by the community, but the automation works fine for me. The only thing I don’t like is that while I can view the status of SimpliSafe’s CO, smoke, temp, and flood sensors, I can’t view the status of its door sensors - and it doesn’t work with non-SimpliSafe sensors.
My TL;DR - Based on my experience, the SmartThings HUB is rarely the problem. However, since I have never used their branded sensors, they could be total crap. SmartThings is a great medium between the inflexible simplicity of a hubless setup, and the super-flexible, but complex world of HomeAssistant. You may need to return a device or two to switch it out for a different brand/type, but don’t give up on the ST platform. It’s a great option once you get it tuned.