Yes it's 1920x1080px. I guess it depends on the kind of work you do and how far away you sit from it. For me it works quite well for graphic / photo editing, but when I have to read a lot of text or am using VSTs with tiny non adjustable GUIs I regularly catch myself leaning forward and killing my back. I do not have these problems when using my 15" macbook pro, but at the same time I couldn't imagine moving the monitor forward on my desk (it would leave me with no physical workspace).
I have found these two websites quite helpful when deciding on which size I should upgrade to:
https://www.designcompaniesranked.com/resources/is-this-retina/
https://dpi.lv/
Regarding scaling: I noticed that scaling up always results in a slightly blurry UI, whereas scaling down (increasing the workspace) stays very sharp - I suspect it has something to do with macOS' internal rendering and is not monitor specific.
I would like to add that I had a 24inch as a teenager (10 years ago) and at the time it seemed enormous, but nowadays with smartphone displays and tv screens growing larger and larger it suddenly appears quite small. A bit off-topic: This is actually a huge problem for me for console gaming; I only have a 32inch TV and can't play modern games comfortably anymore because developers have shrunk the UI considerably, whereas games from 5 years ago appear just fine.
[doublepost=1541108898][/doublepost]Also what you could do to simulate this: If you have Macbook lying around, download "Display Menu" or "SwitchResX". Place your macbook where you would place your monitor and set the resolution to the closest DPI of the 24" Dell (185 dpi). E.g. in case of my 15" Macbook it would be 1024x640 @2x, so 2048x1280px. The macOS menu bar will give you a sense of scale.