That's not a feature flagging service then (config as a service! not a thing really...)
I've done both client and server side implementations of the launch darkly sdk and that's how it's done to know client context.
If you're initialising the entire SDK only to load 1 set of configuration items, I'd argue you can host the config as a json file on a CDN and be done with it - feature flagging is overkill.
All good - it is something that has been over-complicated for marketing/product reasons.
If you know what A/B testing is, feature flagging can really allow you to nail down how you should deliver an experience to an end user.
We track end-to-end engagements on our websites based on how the content is displayed on a page with more performant layouts/content winning the test to drive users through the funnel.
I don't love it though because it's a lot of waste that gets left over and not cleaned up leaving billing to grow exponentially as flags are continually called for no reason.
Guys this is exactly the kind of banal crap that makes a simple app into a monsterous beast that won't work unless it's connected to the internet.