Thanks Manxman78, just me being a little cynical! There always seems to be a callout for marshals for first practice (usually) & I wondered whether this was a contributing factor to the decision to go electronic. 
I can see the safety aspect of them, presumably they're controlled in a foolproof fashion, not by wifi/bluetooth signal jiggerypokery or somesuch thing!
It should also do away with the "i thought i saw a red flag waving" thing that has happened in the past.