Received a HP 8481D today.
Quick check with my HP 3335A shows it's working fine down to -70dB (in fact it goes down to ~-75dB).
A quick check with my cinesium low cost siggen (range: 34MHz to 4.3GHz) shows that it's level is frequency-dependent off in a range from -2dB to +3dB.
I'm happy since I only paid ~122€ delivered.
Now looking forward to checking my new toys to come; two HP attenuators that I'm waiting for being delivered.