Nemo288 gave you the details on the Labradar - I'll only correct him by saying the Prochrono is only a little off from the Labradar . . . if you set the optical chrono up carefully and identically each time.

Nearly equal in accuracy and costing less is the MagnetoSpeed, but it attaches to your barrel so (a) it changes POI and (b) can't be used on many pistols and some revolvers. If you believe in barrel tuners, then the MagnetoSpeed probably also has an affect on group size when attached directly to a barrel.

Unlike the above types, optical chronos must be set up downrange when the range is cold, are negatively affected by changes in lighting, lack of light, and weather, and for most of us require a ready supply of Purple Hearts OTOH, they cost a LOT less and can give you the info you need.

Having a CED M2, a MagnetoSpeed V1, and a Labradar . . . I can tell you there's nothing like a Labradar but it may well be overkill for your actual needs.