The memory consumption of Network Monitor is primarily due to the map. It looks bad, but is not that bad because most of the memory is a cache for rendered graphics. This cache is freed when an other app needs more memory. As long as there is no pressure, the map keeps the cache.
The CPU load is an other issue. We are aware of it and are working on a fix. This high load occurs when you run applications with a particular connection pattern, e.g. wallets for digital currencies or similar.
I suppose this is for Network Monitor. When you close the map and force-quit Network Monitor, it will re-open automatically with the map closed. How much is the memory usage then?
I'm asking because the map is a standard user interface component which is not under our control. It caches rendered bitmap images as long as there is enough free memory. If you have lots of RAM and no other app needs it, that may be a huge amount. It will be freed at the moment an other app needs memory, so it should be harmless.
I'm on version 4.0.5 on High Sierra on a mid-2012 MBPr with 8GM memory, and currently my Little Snitch Network monitor is consuming 7.79GB of memory. Hope this issue hasn't been closed because it's still very much a problem.