Hi there, Alex!
I can provide ExtraHop's perspective. I've been in one major customer's NOC and seen large monitors with SolarWinds dashboards along other large monitors with ExtraHop dashboards. I asked about it and was told that SolarWinds provides the "heartbeat" metrics for the network and infrastructure, and that SolarWinds and ExtraHop provided complementary views of what was going on.
You could think of ExtraHop a listening/translation device, deciphering the content of the communications between machines. We don't do WMI/SNMP or any type of flow monitoring. We're not even inspecting individual packets. Instead, we're reconstructing entire flows and streams and then extracting 2,900+ metrics from the full, bi-directional transaction payload. You can see things like processing time per database method used, which clients accessed a particular shared file, or which Citrix XenApp server is causing slow Citrix login times.
Geek Speak contributor Glen Kemp (glenkemp) has some experience with ExtraHop and may be able to clarify the complementary nature of the two products.
Hope that helps!
Tyson