GTM split zone DNS responses - iRule

I wanted to avoid cluttering up our GTM with a bunch of internal pools, so I ended up creating an iRule for each WIP. We have active/active data centers. One data center has a public range of 100.100.100.x/24 that NATs to a private range of 172.100.100.x/24, the other has a public range of 200.200.200.x/24 that NATs to a private range of 10.200.200.x/24. When the GTM receives a query from a private IP (defined in Topology > Regions), the iRule returns the internal IP (LTM VIP) after the GTM has made the LB decision (chosen the "up" pool member). The iRule has been working in production for close to a year now with no issues. It could probably be written more efficiently but I haven't had the chance to revisit it yet.

when LB_SELECTED {
  if { ([matchregion ldns private-ranges]) && ([LB::server addr] starts_with "100.100.100.") }  {
    host 172.100.100.5
  } elseif { ([matchregion ldns private-ranges]) && ([LB::server addr] starts_with "200.200.200.") } {
    host 10.200.200.36
  }
}