Different things work for different people. As long as you know what you’re getting into and it still sounds good, I think it’s definitely worth trying. The issues with reliability in SmartThings aren’t subtle, you’ll usually know within the 30 day return period whether it’s something that will work for you.
My concern is always for people who just install it based on the marketing without realizing the probable rate of failure or the issues with lack of control if the Internet goes out. Installing a siren in an inaccessible place, as some people do intentionally, and then facing a combination of false alerts and having no way to turn off the system from the mobile app can be a very unpleasant surprise if you don’t know ahead of time that that might happen.
There are also the people who buy it for a second location, sometimes hundreds of miles away, not realizing that the firmware updates can be applied at any time without being able to postpone them, and fairly often require that you manually reset sensors or other devices after the system comes back online.
Manual, on-demand control of a device or SmartApp through the SmartThings mobile app always requires an internet connection to the cloud and cannot be performed locally.
Again, there are lots of threads about those issues in the forums, but if you’re aware of the possibilities and you’re interested in trying it, why not?
If I understand what you’re saying, you’re attracted to the idea of self monitoring. There are a number of purposebuilt security systems in the low-cost range that have self-monitoring, such as simplisafe and abode, both of which have security system features that SmartThings lacks, such as exit delays and more local operation. So I don’t think there are many people who would say that SmartThings has the “perfect features” for a home security system. But it may very well meet your own needs and you may be willing to put up with any deficiencies in order to get a particular set of devices or meet a particular price point. That’s a decision everyone has to make for themselves.
As I said, at our household we like it very much for those convenience notifications which can just be very difficult to set up in other systems. But we do use a completely separate security system that will operate even if both power and Internet are out.
Your house, your choice. As long as you end up with something that you’re happy with, that’s what matters.