TLD: Please allow Heroes'Group Move Bonuses to stack (i.e. add up)!
A Valkyrie, a Ranger and an Assassin walk into a bar at the end of the turn in a newly conquered city...the ranger ask the Valkyrie to take off her boots "War Traveler" and asks the assassin to take off his ring "Agrippas Balanced Ring". She puts both on and goes straight to bed, while the other two scratch their head in wonder. Next morning, right at the dawn of the new turn, she gives both items directly back and all three heroes go on doing their heroic things, enjoying +7 move, until they meet again in the evening and do the same swap thing again...ugh!
No punchline. It is just boring and tedious to always swap the GroupMove items between heroes at the start and end of each turn, in order to get the maximum group move benefits as well as the attacking bonuses. This happens rather often to me, too.
Allowing GroupMove Bonuses from different heroes to stack and add up would destroy this boring and cumbersome task, without changing too much. Sure, the three different boots that yield group move would then stack, but it is probably rather rare to get them all three. A small disadvantage.
Furthermore, it would then make sense to buy GroupMove on other hero types besides Ranger and HorseLords, which I currently never buy. I would consider this a good thing?!
In addition, it could open up the possibility to have items with negative group move modifiers for balancing to take effect.