3456A is great instrument, nicely build, fixable, great display, good keys, math functions...
3457A, big meh, nothing great about it IMO, cheap plastics, extremely shit display and no good keyboard
About everything is inside hybrids on 3457A, even the input switching FETs, so if one of them gets fried for whatever reason, you're screwd
And the crazy input ranging design, had to look in the schematics:
30mV/300mV/3V range => no divider, 30V/300V => 1/100 divider, noise accordingly.
Then goes to "input amplifier" or whatever they thought it would be:
30mV x333 amp, 300mV&30V x33.3 amp, 3V&300V x3.33amp
So the common 30V range you'd use for most stuff is what you get after 1/100 divider & 33.3x amplifier, whereas any sane instrument uses a real preamp for 100mV range and a 10/100x divider on 100/1000V ranges only.
Or even a true 20V range, like in Datron 1271/1281 or Keithley 2001/2002
Get a Keithley 2015/2010 or 3456A, 3457A is trash!