Software to test QoS across hops

Hey all, what I’m looking for is a bit outside my domain, so I might not be sure what exactly to ask for...

We work with clients to provide wireless capabilities at sites in which we sometimes have to piggy back off of their network without the ability to dig into their configurations down.

We occasionally run into issues where VOIP performance is degraded when the network is congested. Client says our equipment is at fault, but we have QoS properly configured on our end.

What we want to be able to do is to test QoS forwarding from an endpoint, through the hops in a client’s network, and be able to show them where in the chain either congestion or improperly configured QoS forwarding is at in case they need to fix their own equipment. We’d like to let an endpoint monitor for a period of time to check when the network becomes more congested.

In my brief bit of research, I noticed that Solarwinds and Thousand Eyes have products that can measure these types of stats, but have no experience in the quality of said software.

Any experience as to what has worked for you for this purpose?