If you have a bad Internet connection, it’s a problem, but most of the problems with SmartThings have nothing to do with your Internet connection. They have to do with random errors in the cloud. This is acknowledged by SmartThings engineering staff, and they are working very hard on fixing it. They’re just not there yet, and it’s not a quick fix.
When SmartThings works as intended, it is absolutely my favorite home automation system. It is flexible, versatile, with an excellent vision and a great community.
The problem is that it is at present a very high maintenance system, with a lot of “minor” errors that pop up every week or two and major errors every couple of months. Since last November I have yet to go 10 days without some impactful failure. These are all situations where something that worked on Monday just stops working correctly on Tuesday. Very frustrating.
I myself am Quadriparetic (use a wheelchair with limited hand function) so I have to pay somebody else to do any maintenance, including “just” opening the mobile app and saving something again. Or resetting batteries on a balky device. Initially I had a lot of stuff on SmartThings, but it was costing me 30 or $40 every week in these kinds of fiddly maintenance issues. So I have since moved any “mission critical” tasks on to other systems. I still use SmartThings for some convenience cases like getting a notification if the guestroom window is open when it’s going to rain, because it just does this kind of stuff great. But I can’t count on it.
If all you want is automated Light switches, get Lutron Caseta switches. If you want to add voice control, you can get either an Amazon echo or use apple’s HomeKit. The Caseta line works with both, and I use it with both. ( it doesn’t work directly with smartthings, though.)
What you can do with SmartThings that you can’t do with just HomeKit is set up rules with multilayer stacked conditionals (if a, then b, but only while C and not D) and you can start adding a much wider variety of devices, including light sensors, pressure sensors, leak detectors, etc. All of which is great except for the instability.
If SmartThings reliably did what it’s supposed to, it would be at the top of my list, no question. But since after literally a year of living with it I found that I needed reliability at the top of my list, I’ve accepted having fewer features in order to have more stability for my primary automations.
But other people will make other decisions. Many people love the power of what SmartThings offers, and they’re willing to spend an hour or so a week keeping it running, and they accept the fact that the lights might come on unexpectedly at three in the morning or the ones scheduled to come on at sunset don’t sometimes. Choice is good, and different things work for different people.