Yes you are choosing to present the Sat and Microwave link as wired WAN. But there is nothing to stop you connecting to one via WiFI WAN. The UBR is a great device and I would argue that you’d prefer to use the lower latency bandwidth over dual 4G if it was available so dual modems will be useful later if not today.
When using 4G/LTE it is always better to use an embedded modem then an external one as you get more control and visibility.
If you really want to used wired WANs then look at the balance 30 LTE. Dual Wired WAN (a third can be added with USB to ethernet) and inbuilt LTE. 400Mbps Dual-WAN Router with 4G LTE Balance 30 LTE- Peplink
Its more expensive than the UBR, and only supports bonding when using SpeedFusion Cloud (you can’t bond to your own hosted FusionHub Server).
SFC Details here: SpeedFusion Cloud - Peplink 500GB for 20 USD
You turn it on by buying a data subscription. Your device then builds a VPN connection between it and the hosted SFC service from Peplink. That VPN is SpeedFusion Capable so multiple WANs can be used simultaneously for packet level failover.
IN general there is a 19% bandwidth overhead for SpeedFusion. And mixing links with very different latency characteristics is not an efficient way to use it. So bonding works great when combining dual cellular, but not when combining cellular and satellite. Its still useful though as it can hot failover gracefully between cellular and satellite links.
To be able to advise further you’d need to list the WANs you have with bandwidth and latency values for each.