Both are comedies with a male duo and a great cast list and plots. With MIU404, it's slightly more serious, yet it's still a comedy (at least the beginning is) and like Dangerless Detectives, the 'real' story doesn't start until around halfway through. MIU404 has more and longer episodes so there is more depth to the characters and their backgrounds, as well as having more time to explore various stories. Though a bit different, both shows are great with good acting and screenwriting.
Both have an eccentric male lead and sensible female lead duo (99.9 is slightly more centered on the male duo) Both are comedies and are roughly the same length, yet the themes behind both shows are different (Legal high: Wanting to win every case, 99.9: Trying to find the truth)