Hi,
The Mobile section on the WebUI is not directly related to bonding. The way it works is:
- Set up connections for both SIM cards
- Set up Load Balancing in the Network → Failover page
The speed of the router with dual LTE should be equal to SIM1 speed + SIM2 speed - ~15 %. This is based on preliminary tests and may change in the future (for the better, I hope :)). However, this increase works only with multiple connections (for example, a group users using the WiFi network), so the speed will not increase for single connection solutions, such as single video streaming.
Peplink's bonding is different. It's used to increase the speed of a single connection by establishing two VPN connections (one for each modem) to their server. Then all traffic goes through the server, thus it can increase the speed of a single connection, but it's dependent on their VPN server's resources as well.
(Disclaimer: I'm not an expert on Peplink devices.)