buy spot, short the perp, and pocket funding for free — does delta-neutral actually work?

the strategy: buy 1 spot, short the same size on perps, so price moves cancel (delta-neutral) and you collect funding when it's positive. I get the theory, but in practice — ① what if funding flips negative? ② fees on both legs ③ spot-perp divergence risk... anyone who's actually run it, did it net out positive, and what were the traps?