Brotherhood Banner, Force Weapons and Hammer Hand

[Pooky]

Question about the Brotherhood Banner for a Grey Knight Terminator unit.

If a unit has a Brotherhood Banner it will automatically pass the test to activate their force weapons. Also, Grey Knight Terminators have a psychic level 1 (so they can use 1 psychic power per turn).

To active/ use a Force Weapon is a psychic power. Now, the question, if I have a Brotherhood Banner in a unit, does this mean they can NEVER use Hammer Hand? The reasoning is that the unit will always be using their Force Weapons by default of the banner being present and they can only use 1 psychic power per turn...

OR

Does it mean that a unit of Grey Knight Terminators will always have their Force Weapons activated and can still get the benefit of Hammer Hand (provided they pass their psychic test)...

[Nurgling Chieftain]

...No.

You may choose to use hammerhand. If you try to use hammerhand, you may not activate the force weapons that round (even if hammerhand fails). If you do not use hammerhand, you may activate the force weapons once you've inflicted at least one wound. This activation will automatically succeed because of the banner. You don't have to use either if you don't want to.

[chromedog]

They still count as using a power by using the banner (they just auto pass it). You still choose WHICH power to use. It's just that if you choose to use the banner to auto pass the test, that's your power done.
You can choose to NOT use it and go for hammerhand instead (if you are fighting horde 1W models where the FW instakill is wasted).