The reach check is probably the best you'll find inside a free anti-cheat currently.
Here are some statistics I obtained about the reach check after conducting some tests against the StrikePractice "Hard" Bot using default Medusa settings:
False positives per 5000 legit hits (140-160ms): 0
False positives per 5000 legit hits (1000+-50ms): 2
False positives per 5000 legit hits (Clumsy Throttle: 125ms, 10% Chance): 5
Lowest detection (140-160ms): 3.5 Reach (3 Alerts)
Lowest detection (1000+-50ms): 3.4 Reach (1 Alert)
Lowest detection (Clumsy Throttle: 125ms, 10% Chance): 3.25 (3 Alerts)
The detections were tested by using correctly calculated reach at different values. The sample size was 50 reach hits. The lowest value I tested was 3.15.
Here's how Medusa's reach check compares detection wise against other anti-cheats that I've tested (140-160ms):
https://i.gyazo.com/09287667550a12584f863b492c36134f.png
And here's how it compares against Verus (1000+-50ms):
https://i.gyazo.com/dd1dccc492b7029359e3a05f5c6c2678.png
It's important to note that Verus was not tested against the StrikePractice "Hard" bot but a real player.
I also have to mention that Medusa's movement checks produced quite a lot of false positives especially with higher latency.
Some aim checks also were producing false positives when teleporting so you'd definitely need to mess around with the config.