The Nexia bridge is a Z wave controller, and you have to pay a $10 subscription fee to use it every month.
The SmartThings hub is also a Z wave controller, but has a one time purchase. And also includes a zigbee controller, which the Nexia does not.
Because the schlage zwave locks are certified Z wave devices, their Basic functions will work with either SmartThings or Nexia ( or any other certified zwave controller) , but you will only have access to some advanced nonstandard manufacturer-provided features with the Nexia service.
Whether those specific features are important to you or not, is just a matter of individual priorities.
As for the whole subscription versus one time purchase thing that's again a matter of individual preference. Subscription services typically provide more installation assistance and ongoing maintenance support. Again, you just have to see what's offered and what do you need it.
If you just want basic lock features for a single-family home which is your own residence, it's unlikely you would need the advanced Nexia.
If you want the lock for a rental property 1000 miles away from you, and you want to be able to change schedules on the fly and have different time schedules for different lock codes, then you may want to look into other options.
There are a lot of people in the community using Schlage locks so I'm sure they can say more about which features they use and why. 😎