Replying to this 8 year old question with the short answer.
The 189 uses a dedicated and custom LCD display. The 189-II and 289 utilized a dot-matrix display that is used to supply all typical characters and specialized symbols.
The 189 II is a completely different system from the 189. The 189 II is most similar to the 289 in all regards, except the 289 having the additional temperature sensor.
The 189 has a nearly instant start up where as the 189-II and 289 boot to an entry page and require a function selection to continue. Selecting the different functions on the 189 is very quick compared to the more complex “choice list” on the 189-II and 289.
You MAY find a nice marketing comparison in the archive documents at Fluke.