There are downsides to every low-cost home automation system. And upsides as well. 
- SmartThings has an excellent IFTTT channel/service.
- There is also an official integration with Google home. Official integration only includes some device classes, specifically switches, outlets, bulbs, and thermostats. No locks or garage doors. However, SmartThings allows you to create virtual switches which can then be used to trigger routines or smart apps in SmartThings, so you get Control of the other device classes that way.
https://support.smartthings.com/hc/en-us/articles/214609826-Google-Home-SmartThings-FAQ
- There is no official integration between SmartThings and nest. There is an unofficial integration which works pretty well.
Smartthings is a very flexible, powerful system with a very active developer community. However, it also has some problems with reliability. The company is very aware of these, and has made improving the platform stability their top priority, but they’re not there yet. Pretty much every platform update breaks something at least for a little while. And you cannot refuse or delay these updates.
When SmartThings works as intended, it is absolutely my favorite low cost home automation system. But for the last year, my MFOP (maintenance free operating period) with it has never been more than nine days. I would expect an MFOP in this category at this price point to be at least six months. So for my needs, they have a way to go yet. I would note however that most of the maintenance it requires is Fiddly little stuff, like resetting a device, and there is often a workaround available. So there are many people who are willing to do that level of maintenance in order to get the flexibility that SmartThings provides.
Also you need to know going in that SmartThings is a cloud-based platform. At the present time, the only thing they can run locally is the official smart lights feature and A few parts of smart home monitor. The mobile app cannot talk to the hub unless the cloud is available, even if they are both on the same local network. (Technically it would be possible, but it’s not the way smartthings is designed.) consequently, if the SmartThings cloud is unavailable, there isn’t even a way to arm or disarm the smart home monitor.
https://support.smartthings.com/hc/en-us/articles/209979766-Local-processing
One of the best features of SmartThings is the ability for customers to add custom smart apps or device type handlers, whether written by themselves or by someone else. However, at the present time nothing that is custom can run locally. That won’t matter to some people, but it matters a lot to others, so again just something to be aware of.
You might find the following thread interesting: