The terms "Load Balancing" and "Bonding" can be thrown around quite a bit and somewhat confusing if you're not familiar with how they work. Cradlepoint routers are compatible with a wide array of 3G/4G modems and higher end models like the CBR400/CBR450/MBR1400 feature "Load Balancing". If your office doesn't have a Cable/DSL connection, or you want as many connections as possible this is a great solution to introduce multiple connections to your network environment.
However, if you demand complete control Peplink/Pepwave 3G/4G Load Balance and Bonding routers emerge as a much more powerful solution offering complete networking control. Entry level models like the Peplink Balance 20 and Balance 30 offer multiple WAN connections and a USB input. High end models like the Pepwave Max 700 give you the ability to Load Balance up to 4 USB modems, 2 WAN connections and a WiFi as WAN connection. In addition to "Load Balancing" the Max 700 also offers the ability to physically bond multiple modems together.
You can find a full comparison of the manufactures "Load Balancing" and "Modem Bonding" here - Click: Comparing Cradlepoint Load Balancing vs. Peplink/Pepwave Load Balancing & Bonding