TIL: You can route specific subnets through specific gateways.

That licensing point is particularly painful when the policy object is something you'd define in a single line on a traditional router. I once reviewed a quote where each unique CIDR in a source-destination pair counted as a separate object, turning a simple ten-line routing table into a hundred billable items.

Your vendor risk assessment mention is key. The SLA for IP migration needs to be tested, not just read. We scheduled a maintenance window to force a failover and discovered the BGP session took over four minutes to re-converge, which was outside the documented "seamless" window. The provider's support had no visibility into that delay until we provided the route server logs.