qrp.ddc,
I purchase cables of unknown quality at hamfests and the nanoVNA has paid for itself in helping me avoid selecting cables that physically looked fine, but from both cable ends looked like virtual shorts using the nanoVNA TDR function. With your access to better equipment, the nanoVNA's TDR function probably does seem like a toy, but if the user realizes its limitations and doesn't expect laboratory quality from a $50 device, the function is still a worthwhile tool and learning feature. If the TDR function tells me that a reel of cable marked 25 meters is 24.5 meters that's close enough for me to feel confident purchasing it. Carrying a laptop with me to do the same TDR measurements is in-convenient, although at home I do use NanoVNA Saver to perform TDR measurements. With the multiple firmware versions that have appeared on the scene, maybe one of the developers will branch off a version that removes the TDR function and implements the features you would rather have. That's the great thing about open source projects, the source code is open to modification however it suits each of our individual needs.
Herb.
