If you don't like trackballs, you're out of luck. Watch out for the battery contacts too. A test is to press on the left-hand palm rest firmly when the Duo's running on battery power. If the power goes down, it means the battery contacts are faulty. Again, one that should be avoided.
Some people wedge something thin into the battery bay to make the battery fit in more tightly.
Their lightweight design makes them perfect for road trips or between office and home. They are viable alternatives to the PowerBook 140 and 170 as the Duo 230 and 250 run 33MHz CPUs versus the 25MHz 170 and the 16MHz 140. They also have better screens than the earlier PBs. Their greyscale screens are adequate for viewing graphics and the 250's active matrix display renders greyscale particularly well. Their superior RAM capacities to the 100 series also make them more upgradeable.