I have one of these (rarely use it now as I have a NI GPIB-ENET/1000 which does away with the USB connection in favor of the LAN). I'm fairly certain that these are all clones of the actual device or at a minimum the 3rd shift run.
That said, mine worked flawlessly for accessing my gear. To get it to work you will need, as egonotto noted, a VISA library. You will also need to use the driver and the only way to get that is to install the Keysight VISA implementation (to use NI-VISA you'll need to install the Keysight one in secondary mode and even then the whole system is flaky). You can get all the bits for this from the Keysight website here:
https://www.keysight.com/en/pd-1985909/io-libraries-suiteWhat this will give you is the ability to use an application that calls the VISA API to communicate with a piece of test gear. You can also write your own software using something like Visual Studio 2019 Community Edition (free) and those APIs.
This just gets you to the point where you can start issuing commands to the device and extracting data. Those commands are covered in the Programmer's Guide (located here
https://literature.cdn.keysight.com/litweb/pdf/54622-97038.pdf?id=1000002818-1:epsg:man). It really is quite easy to do using the API - For example here is a C# code fragment from a utility I wrote for the 3325B:
// Setup variables
string SigGenAddress = @"GPIB0::10::INSTR";
string THDMeterAddress = @"GPIB0::1::INSTR";
ResourceManager ResMgr = new ResourceManager();
FormattedIO488 THDMeter = new FormattedIO488();
FormattedIO488 SigGen = new FormattedIO488();
AmplitudeCalibration AmpCal = AmplitudeCalibration.Off;
bool ACUnset = true;
int NumMeasurements = 0;
// Create the datafile
StreamWriter ReportFile = new StreamWriter(Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments) + @"\3325BHarmonicDistortion.csv");
// Setup the VISA connection for the Keithley 2015
THDMeter.IO = (IMessage)ResMgr.Open(THDMeterAddress, AccessMode.NO_LOCK, 2000, null);
THDMeter.IO.TerminationCharacterEnabled = true;
THDMeter.IO.Timeout = 20000;
// Setup the VISA connection for the HP 3325B
SigGen.IO = (IMessage)ResMgr.Open(SigGenAddress, AccessMode.NO_LOCK, 2000, null);
SigGen.IO.TerminationCharacterEnabled = true;
SigGen.IO.Timeout = 20000;
// Initial HP 3325B settings and get the IDN to confirm its connected
SigGen.IO.Clear();
SigGen.WriteString("*RST;", true);
SigGen.WriteString("FU1;", true);
SigGen.WriteString("FR100HZ;", true);
SigGen.WriteString("AM999MV", true);
SigGen.WriteString("*IDN?;", true);
System.Threading.Thread.Sleep(1000);
string temp = SigGen.ReadString();
Console.WriteLine("3325B ID is: {0}", temp);
// Initial Keithley Settings and get IDN to confirm its connected
THDMeter.IO.Clear();
THDMeter.WriteString("*RST;", true);
THDMeter.WriteString("*IDN?;", true);
System.Threading.Thread.Sleep(1000);
temp = THDMeter.ReadString();
Console.WriteLine("2015THD Meter ID is: {0}", temp);
To get the data into another app you will need to work out what the preferred way to do that is - For example you could save the waveform as a set of data points into a CSV file and then read that in, or you could have the device specifically grab a single measurement and then pipe that over to the other app.
Hope this helps,
TonyG