Massage guns
Evidence: limited
Good for a short-term boost in range of motion and for feeling looser, but with little evidence they speed real recovery or improve performance. A comfort tool, not a necessity.
Keep it in proportion
This is one of the last few per cent, at most. It pays off only once the basics are already in place: consistent volume, sleep and adequate fuelling. Most runners gain far more from those than from anything on this page.
Percussive massage devices apply rapid mechanical taps to muscle. A systematic review finds they reliably produce short-term gains in range of motion and flexibility, with acute increases in hamstring range of motion of up to around 11%, and can modestly ease perceived soreness (massage-gun review). Beyond that the case thins out: effects on the recovery of strength and endurance are mixed to null, and using one immediately before strength, power or sprint work is not recommended, because the acute looseness can blunt force output.
This places the massage gun alongside the rest of the recovery modalities: a genuine but largely acute and perceptual benefit, not a demonstrated acceleration of physiological recovery. That is not a reason to avoid it, feeling looser and less sore has value, and the devices are convenient, but it is a reason not to treat it as essential or to expect it to make you fitter or faster. If it helps you move and feel better before or after a run, use it; do not buy it expecting a training effect.
As with any tool for tight spots, recurring tightness in the same muscle is better read as a sign of an overloaded or weak link than as something to percuss away. The durable fix in that case is strength work on the cause, not repeated treatment of the symptom (see massage).