Some interesting ideas there. I've always used the edge-then-flag method with both arcs and LEIs but I'd flag to the bottom tip with the foil and top tip with the LEI (flips it round and dumps it on the beach pointing the safe way!).
In the past I've had the safety jam on the bar while releasing and spiral me down the beach, I've had the flag out line snap trying to water-ditch it (Arc 1120 in 25kts) and spent about 100m dolphining through the sea toward the beach. Any idea of back-stalling a kite in higher winds gives me red flags, Id rather risk flagging and stretching 10 euro bridle set than be eating a fence or (as is my current spot) an electrified railway near the back of the beach
That said, I've not tried the Speed5 yet but 12m^2 of fabric is going to pull like a train regardless of how it's held unless it's flagged.
I've got an infinity 3 airstyle bar which seems to release to the front line to flag - looks like this has the potential to hold some power despite loss of the other 3 lines (I've had this arrangement on a previous smaller foil and the bridle held the shape of half the kite pretty well at decent power!). I'd much prefer to flag to a rear but that's not the design.