@madvinegar 

I assume you want WAN side LAGs?  Does your upstream device support LACP?

  @madvinegar 

Then you mis-understand feature of LAG or (switch) port channels.

What you are asking for is bonding disparate internet connections...and this requires an aggregation/de-aggregation node at both ends.  In your case, what you are asking for, I think, is to add your VDSL connection to your LTE connection and make a single pipe out of it.  Solutions like this do exist, but they depend on an internet connected node, typically in a cloud like AWS that has TWICE the maximum bandwidth you can expect from your two connections.  

What then happens is an application on your LAN connects through the local aggregator (what you envisioned as the ER605).  That device divides the user traffic across both connections based on their then-available BW (LTE will fluctuate).  Both streams transit the internet and arrive at the cloud-based aggregator node, which then recombines the user packets in their original order and (note this process makes the overall connection slower than the slowest of your connections) and sends them back out to the internet as a single flow.  Since the traffic hairpins through the cloud node, you need double the internet BW there.

This is a lot of effort and expense for little if any benefit, because as latency increases you max available BW will decrease thanks to TCP windowing (Google it).