I dunno - I've found it useful on a bunch of images[1] but I tend to try Pixelmator Pro first because that's a simple key combination to enlarge an image and 90% of the time it's Good Enough for my purposes.

[1] The new Photo AI, on the other hand, is slow, clunky, and not infrequently glitches out wildly. But on the plus side it does combine sharpening and denoising into one workflow.

I was super unimpressed with the 1.0 release of Photo AI; in particular, the sharpening was a LOT slower than standalone. But that's fixed now, and unless Topaz starts backporting the improved models to the standalone tools -- so far, they have not -- Photo AI will get you better results.

I spent a lot of time last month using Gigapixel (actually the improved version in their new Photo AI product) last month on dozens of images for my dad's memoir. There were a couple failures where the input image was just so blurry or low-res that it couldn't be saved, but Topaz significantly improved image quality while upscaling in 90+% of cases.