As discussed in other threads the Unchained Monk has some archetype compatibility issues.
In order for my players to keep their current characters rather than rebuild from scratch would letting them use the Qingong Monks trade out to get access to the Unchained Monk Ki Powers be fair?
They don't want to lose that Will save.
Thoughts?
The Ki powers of the unchained monk are nice but the really useful changes are the flurry of blows and style strikes. Other than the Zen Archer the unchained monk is a lot better. The will save is not as much of a problem as it seems. The monk is a WIS based character so even with poor will saves he still has above average will saves. Still mind gives them +2 vs Enchantment spells and effects which covers most of the will saves except for fear.
I actually found that many of the Ki abilities of the unchained monk are weaker than those of the normal monk. Diamond abilities are all limited duration and Diamond Body is changed from flat out Immunity to being able to neutralize poison on himself by spending Ki.
I would allow a player to use the new system for Ki, but he has to use one system or another. So if he wants the new Ki power he replaces all of the Ki power. He can’t for example keep the old Diamond Body and still take Elemental Fury.