I have three dogs ranging from 60lbs to 90lbs. I’m not real worried they’ll get out. When my concrete guy foleft the side gate just a bit open by mistake one day, only my female went exploring. I did not notice until I called them back in and only 2 responded. When I went looking I noticed the partly open gate and realized what happened. A quick run out front and a call of her name made her appears from around the corner and come right back. They know who feeds them and puts a roof over their head. 
They also wear their collars 24/7 and have ‘contact info’ tags on them. As well as being microchipped and having that registered with Animal Services. So if they get picked up by the county, they wand them and I’ll get a call.
I don’t like the ‘pay per month’ solutions as that adds up with 3 dogs. I would like a warning if any of them breach the ‘containment zone’ so I can take action. Maybe the Smartthings tag will work, maybe it will not. There’s just not enough info on the site for me to base a decision on. I’d love a smartthing to let me know if my garage door is open or closed or if I have a water leak at my water heater, sink or bathrooms. Again, not enough info on the site to make an informed decision on if they will work.
On the other hand, the thread about smarttags looks very promising for some of my needs. At least the site has a bit more detail. But I learned a while back to stop being an early adopter as it can get costly. With age comes wisdom. Sit back and wait what happens for a little bit.