1: Every species and every era has a different transporter effect. Do we know why they are different?
The different effects for different species is simply so we the audience know who's doing the beaming. The ever-changing special effect for Starfleet's transporters is due to different FX teams, different producers and advances in real-life special FX technology. They all represent the exact same thing in-universe in the same way Kirstie Alley and Robin Curtis represent Saavik, or William Shatner and Chris Pine represent James T. Kirk.