I tried out the new 3X update in Katamari Damacy Reroll, which is locked to 30 FPS, and it worked surprisingly well.
I played one of the final levels that are 20 minutes long, and even by the halfway point, toggling lossless scaling off started looking like a slideshow.
I've struggled with motion sickness a lot in this game, and it definitely helps.
At the same time, you have to not look too closely.
While it is a lot smoother, the interpolation artifacts are kind of obvious too.
The other thing that surprised me was how… okay 90 FPS was at 120Hz.
When dealing with games that can run natively at 90 FPS, but have a camera that updates at multiples of 60 (e.g. Dishonored 2/Deathloop) or have VRR disabled, I would generally say that capping to 60 FPS produces a smoother image than 90.
But here, interpolating to 90 seems preferable even though VRR is not active. 60 is noticeably less smooth.
It could also be that the starting point of 30 FPS is just so bad that 90 starts looking better regardless of whether there's some slight judder remaining.
It does seem important to use an external frame rate limiter to set your target frame rate, as games will not be properly smooth unless the frame-time chart is perfectly flat.
And only the DXGI capture method seemed to work properly at 3X.
Like DLSS/FSR3 frame gen, I would choose just about any alternative to get natively higher frame rates first.
If dropping to DLSS Ultra Performance will get me 90–120FPS natively, I'll take it over interpolation any day.
But if it's a game where the frame rate has a hard limit, or nothing I do can improve the frame rate further, it's a nice option to have.