The 1ms they quote is what we call Grey to Grey. It's basically a made up bullshit useless measurement. It's not even measuring how long it takes a pixel to go from Black to White (or vice versa) but between a lighter and darker Grey.
While a faster pixel response CAN sometimes reduce issues like note ghosting (where a moving note seems to leave a phantom version of itself where it was last frame because the pixels haven't fully changed back to the background color yet), in order to achieve the 1ms they quote for an IPS panel, they need to "overdrive" the signals to the pixels. Basically they need to apply a higher voltage than the pixels need. The higher the voltage, the faster they will switch. But it comes with potential drawbacks in image quality.
https://blurbusters.com/faq/lcd-overdrive-artifacts/ This page is a good place to learn about the potential effects of overdriven pixels. And yes, I can guarantee 100% that the 1ms time they quote requires overdrive, because IPS panels simply cannot normally respond that quickly.
But yes, if you are planning on doing more creative work, I suppose an IPS is a decent choice for that, but you are definitely sacrificing some of the benefits of a TN panel, such as not needing overdrive.
The only difference I saw between the monitors (note: I didn't look at anything beyond the base features and specs, didn't check IO/inputs etc.) is that the second one supports Freesync, which is a nice feature, but won't likely make any noticeable difference in mania. Even a fairly week PC should be able to run osu at framerates that exceed 75fps, which means that Freesync here would do absolutely nothing. And on top of that even without freesync, tearing is not really a noticeable issue in mania because the note motion is vertical, so even assuming you had tearing, you'd likely never notice it since tearing is only really noticeable during fast left/right movement.