I've used them both.
The underlying network analysis functionality of TC is provided by the NetGuard Firewall, developed by Marcel Bokhorst.
In my experience the significant difference between the two is TC ad-blocks using host files.
NG provides more granular control of access denial to your Wi-Fi and/or mobile connection.
I think both are good apps for the privacy aware.
I understand this is confusing. The fact is NetGuard is a VPN. The 'only' difference between ExpressVPN and NetGuard is that the former is hosted in ExpressVPN's data center, and NetGuard is hosted in your phone.
You can only use one VPN at a time per Android device.
You have to choose, which machine do you trust the most, the one in your pocket or the one owned by strangers.