That monitor has a 12 inch screen, compared to a classic Mac which has 9 inch screens, including the Color Classics. The Color Classics are about equal in size to the Classic Macs with 9 inch screens, it is the 500-68K and 5000-PPC Macs that have the huge 13 inch screens.
You stated 68K, the Duo 2300 is PowerPC. All the Duos from the 210 to the 280 are 68K. But within that realm, it is the smallest Mac of the series. If you are afraid in using it, you can get a 4-8GB CF with a CF-to-IDE adapter or a small 4-8 GB IDE SSD (note: not all will work with it) for and make it solid state. It would also make it faster. Just remember, that screen is a bit on the small side. If you can use a PowerPC, go with a 1400, with the same CF/SSD set up - it would be faster.
LCs are the smallest Macs if you do not consider a monitor for them. Add a monitor and all that business about "small size" goes out the window. Now if you can get an LCD screen to work with it... then maybe...