The Einhander style is probably the worst of the lot, you don't get the big damage or reach from two handing, you don't get the virtual accuracy(2 attacks being more likely to hit at least once) from TWFing, you don't get the AC from sword and board. Of course it makes some sense(nobody fights that way unless they're doing sport fencing or have no other choice), but it'd then be focused on a lot of quick, light attacks trying to nail a vital spot thematically.
Spring Attacking has several major problems:
-Light armor, making them piss easy to hit in contrast with the thematic agility
-Constant AoO provocation, they don't usually have reach either.
-Thematic association with the einhander style. To add fuel to the fire.
-Weak impact. At least Flyby Attack gives you a full standard action to deliver your offense, which you can leverage with powerful standard attacks(like spells)
-Not effective even at what it does. Sure, you're supposed to move in, stab them, and move out, which prevents your opponent from getting a full attack off...except you're splitting your move speed into two intervals, and if it's 30ft, you get to move 15ft in, then 15ft out again, leaving you with 1 AoO and nicely in Move+ Attack range, and to spare. Or worse, leaving you straight up great to be ubercharged.