That’s a lot of different questions! With a lot of different answers.
First of all, outlets are not usually part of a home monitoring system, that’s mixing home automation with home security. So it complicates the answers.
Second, “good“ and “inexpensive“ are usually two different things. So you need to be a little more specific about what you mean by both of those. There are devices which are pretty good given how inexpensive they are. And devices which are good but cost significantly more than the cheap ones.
Most people who want some kind of home security put reliability as their top priority. Once you do that, the cost of individual devices generally goes up.
Smartthings Itself is primarily a cloud-based system. There are a few things that run locally, but not really very much. And probably a lot less than you expect. Just as an example, if you get the Samsung SmartThings Hub And the smartthings cloud is not available, either because it is down or because your Internet is not working, then The mobile app won’t work at all and you won’t be able to either arm/disarm any of the security features.
The much better alternative if you are looking for a security system (and the one you will find if you follow any of the links labeled “security” on the smartthings site) is the dual logo ADT/smartthings security panel. That system has a lot more stuff that can run locally, and also has cellular communications so It can send you notifications even if your Internet is out. But you have to use its own dual logo sensors with it. And that system costs more than the basic smartthings home automation system.
Anyway, you put all of that together, and we would really need to know more about your own priorities before we can answer the questions you raised.
If you primarily want a security system, even a self monitored one, then you should really be looking at the ADT/smart things security panel and comparing it with other low-cost security systems like Abode, Simplisafe, Scout, etc.
If you want to spend as little money as possible and you’re OK with a cloud-based system with less reliability, then we can talk about options using the Samsung smartthings hub.