The S27H80 is a fantastic office monitor with a great price-performance ratio. The input lag is effectively not stated anywhere and in practice also depends on the input used and the cables. However, I think the lag is hardly the fastest (my estimate is 16-18ms). Definitely not an issue for everyday office use and easy gaming! For intensive gaming, I would probably choose a different product, also because of the response time. For video and image editing I would also choose something else, not because of the lag, but because of the colour space and colour fastness (we are very satisfied with a BenQ SW2700PT).

Since I bought the monitor primarily for image processing and need a reproduction that is as true to colour and as close to reality as possible, I am not interested in the input lag. This is probably more interesting for gamers.
For my purposes, this monitor is perfect. It's the best picture I've ever had!