Grayy_ Hello. Were I in your situation, I'd opt for the Dell S2721DGF(A) for only £9 more. It uses the same LG panel, is 165 Hz, and is tuned slightly better than LG's version. If you happen to have an Nvidia GPU, then make sure to use either new panel with a DisplayPort cable, so that g-sync compatibility is enabled.
Dell S2721DGFA 27 Inch QHD (2560x1440) Gaming Monitor, 165Hz, IPS, 1ms, AMD FreeSync Premium Pro, NVIDIA G-SYNC Compatible, HDR 400, DisplayPort, 2x HDMI, 5x USB 3.0, 3 Year Warranty
£329.00
Addendum: Also check the price on Dell's UK site, as it may possibly be cheaper there.
Hardware Unboxed: Dell S2721DGF Review, The New 1440p 165Hz Gaming Monitor Champion
View: https://www.youtube.com/watch?v=D3vbqyjgPpY
FYI: I own two of the 27GL850's, which were released in 2019. It's my understanding that the 27GN850 was the 2020 rebranding of the same model. I don't think LG changed anything about the actual panel, and the only difference that I'm personally aware of is that they moved the red racing strip on the legs from the back to the front. I also own one 27GP850, which was the 2021 refreshed model.
Reddit: Difference between "Dell S2721DGF" and "Dell S2721DGFA"
* According to comments, the 'A' variant includes updated firmware and potentially an added monitor arm. I'm not sure about this last point, so I'd appreciate if you confirmed this point, if you happen to order it.
View: https://www.reddit.com/r/Monitors/comments/jmnmia/difference_between_dell_s2721dgf_and_dell/