The iPad Pro (12") I ordered ‘just to see’ what it was like arrived yesterday… and I really didn’t want to like it, but I do 
After @mindriot (and several others) recommend the Apple Pencil so much in this thread: iPad for reading programming books? I ordered one of those as well (with the 11" that arrive a couple of weeks ago) and I have to say it is brilliant - especially - on a 120hz screen which the iPad Pros have. I used it to create a portrait of my niece and I really enjoyed working with it. If you’re curious why the pencil is so expensive and why it’s worth it, check out this video.
Going back to your particular use case tho:
If it costs just £170 and you are happy with a non-HiDPI monitor, it sounds like pretty good value 
However if you have a Mac, and want/need an iPad, the convenience of an iPad and things like sidecar is just so appealing. No need to connect any wires it does it instantly and wirelessly, and you can sync things like Notes, browser tabs, contacts, messages, books, etc, again, instantly.
For me the 12" iPad is definitely better than the 11" too - you get much more of a desktop like experience in terms of web pages and books, and when taking notes in bed I rest it on my belly but with the 11" I had to lift it because it was just too low in the same position (so not as comfortable when taking writing notes). However the main disadvantage for me is that it doesn’t let you mimic the screen width resolution of smaller iPads - which would have been super convenient for testing apps.
Every time I have reached for an iPad I have always picked up the 12" too - which definitely tells me something. It’s also brighter but the display of the 11" is pretty amazing too. It does have some issues with ghosting (mini-led is definitely not as good as OLED on that front) and it does have a darker area around the edges, but these are just niggles and both screens are excellent - but the size of the 12" is definitely nicer and I’ve hear a lot of people say that it makes them want to use it to ‘work’ much more than the 11" which they generally prefer more to consume content. I would be happy with both and I am still not sure whether I want to spend this much on ‘just’ an iPad! Especially since Apple could have made it run macOS now it has Apple silicon!!!
Sorry I seem to have gone off-topic a bit