I believe most people are plugging these directly into the front end of their 1meg scope inputs w/o 50 ohm termination.
However, some of the ads for this device show over/undershoot on square wave. I'd hope there vendors would be presenting the unit in its best possible light.
I'll be able to confirm shortly. I just ordered the 5MHz model (hope I can convert it to 20MHz), and I'll run some tests when I get it. Spectral purity, THD, phase noise, etc.