Eh, I built a feature flagging system for service with millions of daily active users and it: wasn't hard to do, was easy to extend to support targeting, segments, and progressive rollout, and on top of it flags are easy to cache, so the database pressure was not that big. We did this long before LLMs, and it occupied maybe a month of engineering time for me, here and there as we needed new features, while I was doing other things. We did choose the wrong hash for bucketing in the beginning, but we noticed the stairstep patterns in our buckets quickly (an advantage of having millions of requests per day to measure) and picked a better one. It was much better this way since it meant backend flags without a roundtrip to a 3rd party service (that was the main motivation, we wanted this kind of control without adding latency to our requests). I remain baffled by launch darkly or other such services. And today, with LLMs, just build it yourself is hard to argue against.