So the probe is great when your client has a machine that's on 24 x 7 (such as a server as opposed to a workstation) but with many clients going to completely cloud-based environments, it can become a bit more difficult to dedicate resources to a probe machine.
raspberry pi units all in including storage cost around $60-$70, and are perfect to act as a probe unit that can be put at a customer site in a network room, closet, etc. It makes all the sense in the world to be able to deploy an RPI unit at a client site in a network closet and not require any client-side specific resources.
Finally, because it sits outside a customer-owned device (such as a server or workstation or anything else), you can independently monitor the network and if an issue arises on a server, you can be alerted of a problem beyond a simple "probe not reachable" - you can see what's going on with the network regardless.
I understand that there was a probe that was Linux based in the past - maybe it's time to bring it back and customize it to an RPI.