The Radio Slave 4i offers these refinements and features: Range up to 350' (200' with antenna down) Hot shoe mount for the sender unit. Radio slave also mounts to brackets, shoe mounts, etc. Instant retriggering for multiple flash bursts(no waiting between triggers as with infra-red slaves)Faster than any motordrive firing sequences Battery life increased five times Remote unit: 400 hrs. (alkaline) 800 hrs. (lithium) Sender unit 1-2 years Fastest sync speeds: 1/500 (focal plane) 1/1000 (leaf) This extremely fast sync means Radio Slave 4i is indistinguishable from wired sync.