The GCU2 is a SOLID board and the new software gives better control. It would not be a bad choice for those needing 3 or less power level.
For myself, the Heliboard makes more sense because I have every caliber and switch those plus projectiles frequently. The ability to fine tune AT ANY TIME with the voltage is great plus 12 power levels instead of 3, PLUS more info on the display including BATTERY VOLTAGE... for the life of me don't know why that's not on the factory board.
Pro..
GCU2 - timeout, (no battery damage)
Heliboard - no timeout, display information, 12 power levels, programming from the trigger
Con...
GCU2- removed from stock to program, timeout(hunting or competition), limited display info, more expensive, separate programmer
Heliboard - no timeout (will KILL batteries if left on), MAY be more limited for speed cycling
They are relatively equal in power and build quality plus support so these are my views on the tradeoffs. They are relatively equal to switch between power levels or other options, also. A note on board operation that may affect speed... the GCU2 is always on till it times out... cycling the bolt does not shut it off , ,, the Heliboard is completely shut off each time the bolt or safety is cycled...it must charge or finish charging the caps when turned on or bolt closed. Jack gives a 150 millisecond charge time but we've seen longer on some boards. They're well less than a second, worst case, anyway .
Hope this helps,
Bob