Just for completeness, shown sweeping the homemade buffer to 1GHz. Not a real good test setup but gets us in the ballpark. Peaks up to 1.5 dB and starts to drop like a rock above 200MHz. -3dB is around 300MHz.
Really, for the 50MHz high end mentioned and sweeping filters I would have just went with that little NanoVNA. I've played a bit with them and even for narrow band work, they seem pretty decent depending on how low a noise floor you need. Worse case, a costly repair is limited to the time it takes to get a new one shipped and $50.