A1) An isolation barrier maintains galvanic isolation between the hazardous area wiring and the safe area wiring whereas the other type does not, which may be important depending on the type of instrument connected.

A2) Both types can be used, though it depends on what the device is connected to as to the correct type. In each case, follow the instrument manufacturer's instructions to the letter.

For DI,DO,AI,AO isolation, separate with an isolation barrier.

If you are routing cables in tray, use of an isolation barrier (divider) between your digital/analog I/O will be fine.

If in conduit, separate D/A conduit systems is a must.

If in a panel, individual Panduit channel to separate the looms will suffice.

If you are in a classified area, tray cable sealing glands and/or conduit seal-offs are a must.