Arstechnica does a write comparing Apple, OZone, LANDR and Bandlabs AI Mastering Assistants.
I liked most of the results I got. Mastering Assistant, Ozone, and LANDR were each clearly capable of pro-sounding results; the web-based services I tried, including Bandlab and Waves, were somewhat more variable.
Apple's Mastering Assistant offered a less compressed and more open sound on my demo track, which sounded very nice. (Indeed, on another track of mine, I preferred Apple's approach for precisely this reason.) LANDR was also great, though it offered a much more controlled sound. For this demo track, however, Ozone's compressed-but-not-completely-crushed sound and its excellent handling of the overall EQ (the highs were present but never sizzling, for instance, and it dealt with one or two moments of sibilance better) won me over.