Great anti-cheat, especially considering it's free and supports basically all spigots (1.8-1.19), all client versions, a lot of different client mods and server plugins. And the version support is unlike other anticheats I've tested where the anticheat just runs on the advertised versions, Grim's version support also ensures that there are very few false positives and the detections stay strong.
When it initially came out it had some flaws but even then the reach detection speed was well above any other anti-cheat available on the market [1] (Not sure about sparky, never tested it) and false positive wise it used to be only slightly worse than anticheats like Karhu, Kauri Verus and Medusa [2], where most of these anticheats came with a buffer by default and grim didn't back then.
I tested it recently and it seems to have improved since the last time I tested (Version 0.0.1), now I could not get the reach check to false flag even at 0 buffer and by doing some not very well known bugs and only falsed the simulation check a couple of times.
Sure Grim doesn't have ghost detections but movement and reach wise I don't think you can get a better anticheat than grim right now (no matter the price), although I have not been keeping up with all the newest anticheats after about september 2021.
PS: I might be biased as I have helped and been helped by the developer of grim a tiny bit, but I tried to stay neutral.
[1]
https://cdn.discordapp.com/attachments/841062335682445322/887916049054461992/703e7280ca9a0643125357e7d769b3f3.png
[2]
https://gyazo.com/c70f8066a39b096e8138c898ecefe0f3