The Universal Buffer is a stereo buffer. It has unity gain (with options to increase the gain by adding a resistor). It features a single-ended output as well as a differential one and you can use both outputs at the same time. The Purifi/Hypex Buffer is optimized for the Purifi 1ET400A and Hypex NC500. If you were to connect a Universal Buffer to a 1ET400A or NC500 and configured it for the same gain as the Purifi/Hypex Buffer, you'd get about the same performance as with the Purifi/Hypex Buffer.
So I am aware of the extra circuitry to allow a single-ended output to work in parallel to the differential one – and the fact that it is stereo and not mono. I was referring to the core circuit, the one that is on the Purifi/Hypex Buffer – that one seems to be the same, right?
There is also a difference in declared slew rate between the two: is this due to a different RF filter implementation or was the information in the Purifi/Hypex Buffer case given for the circuit without the filter?
Indeed I have connected the Universal Buffer to a pair of 1ET400A's, using the prototype boards as breakout boards. Just to complicate my life and because I already had the Universal Buffer...