No catch. We just got tired of endless sales-calls and 100 SaaS companies trying to upcharge us for everything. Prefab is different. We are developers, building webscale killer versions of these core systems so that we never need to do it again.
Each server will setup a streaming connection to our servers so that updates propagate close to instantaneously. We monitor how many connection there are every minute, aggregate that and charge a dollar for each.
Sure. You've got 10 servers. 10 engineers and 5 product people. Servers will be $10 for the month. Engineer laptops will connect during development. If they are active 40hr/wk that will be ~$3. Product people may make 50 changes to flags, so that's another $1. Net: ~$14 for the month.
The server SDKs will all download the configuration and then evaluate it as many times as they want. Mobile and web clients won't download the config. Instead, they'll ask the server to evaluate the feature flags for each request. We charge $1 for every 10k of these requests. Depending on your architecture you can absolutely use your own server SDK instead of making these requests.