How to Choose a Feature Flag Tool

A guide to selecting the right feature flagging and experimentation platform for your startup. Covers progressive rollouts, A/B testing integration, pricing at scale, and when to build versus buy.

Key Decision Criteria

Feature Flags vs. Full Experimentation

High Priority

Basic feature flags (on/off toggles, percentage rollouts) are table stakes — every tool handles this. The real differentiator is experimentation. PostHog and Statsig include A/B testing with statistical analysis. LaunchDarkly focuses on operational flags and progressive delivery with experimentation as an add-on.

Pricing at Scale

High Priority

PostHog offers 1M feature flag requests/month free, then $0.0001 per request. LaunchDarkly starts at $10.50/month per seat with limited MAUs on the starter plan. Statsig offers a generous free tier (up to 1M events/month) with usage-based pricing after. At 10M monthly requests, the cost difference between platforms can be 10x.

SDK Performance and Latency

Medium Priority

Feature flag evaluation happens on every page load or API call. Client-side SDKs that phone home on every evaluation add latency. LaunchDarkly's SDK uses a streaming connection for near-zero latency flag updates. PostHog and Statsig use local evaluation with periodic syncs. Test SDK performance in your specific environment before committing.

Questions to Ask Yourself

Do you need just feature flags or full A/B testing?

Flags only (kill switches, gradual rollouts, beta access): PostHog's free tier or a simple JSON config file may be all you need. Don't buy LaunchDarkly at $10.50/seat/month for basic toggles. Flags + experimentation: PostHog and Statsig bundle both — you get flag management and statistically rigorous A/B tests in one platform. Enterprise feature management: LaunchDarkly's targeting rules, approval workflows, and audit logging are designed for large teams managing hundreds of flags across environments.

How many monthly active users does your application serve?

Under 10K MAU: Every platform's free tier covers you. Choose based on features, not price. 10K-100K MAU: Pricing starts to matter. PostHog and Statsig's usage-based pricing stays reasonable. LaunchDarkly's seat-based pricing means a team of 5 engineers costs $52.50+/month regardless of usage. Over 100K MAU: Model costs carefully. PostHog charges per flag request, so evaluate your request volume per user session. Statsig's pricing becomes very competitive at scale.

Do you already use a product analytics tool?

Using PostHog for analytics: Add PostHog feature flags — the data is already unified, and experiment results connect directly to your analytics. You avoid integration work entirely. Using another analytics tool: Statsig or LaunchDarkly integrate with external analytics but require event piping. PostHog's all-in-one approach may justify switching your analytics too. No analytics yet: PostHog gives you analytics, flags, experiments, and session replay in one platform — a compelling bundle for startups starting from scratch.

Red Flags to Watch For

Accumulating stale feature flags without a cleanup process

Feature flags are meant to be temporary. Every long-lived flag adds branching complexity to your codebase and cognitive load for developers. Establish a rule: after a flag is rolled out to 100% for 2 weeks, remove it from code. LaunchDarkly includes flag lifecycle tracking — but process matters more than tooling here.

Building a custom feature flag system instead of using an existing tool

A basic flag system (if/else with a database check) takes a day to build, but it doesn't include targeting rules, percentage rollouts, audit logging, or SDK performance optimization. PostHog's free tier gives you 1M requests/month — more capability than a custom build, with zero maintenance overhead.