I have two of them that give acceptable results when viewed with a NanoVNA & a trusted 50 ohm load, but the results could clearly be better. 

I want to put one at the tower for my VHF/UHF satellite array, run one feedline to the shack & use the second one to split the 2m & 70cm signals back out to go into the radio. Inserting two of them into the chain only makes the overall response worse, so the desire to improve the tuning is greater.

These things are seemingly well built; all metal enclosure with the lid soldered in place, so accessing the internals will be a bit of a chore. It occurs to me that having the lid off may influence the results.

I thought I'd ask here before attempting surgery. Sweeps attached...

Anyone?