*Very* good.
People tend to ignore it, but I think it is a must have for power gamers.
Speed kills. I have a nezumi (40' base speed) ranger archer with the quickness trait (+10' movement). When he casts longstrider (+10' movement), he gets going up to 60'. I'm thinking of taking a level of cleric (or a prestige class that allows turning undead) to get this feat to increase that up to 70', though his charisma is only a 12. When hasted, that would bump up to 90'.
Even when he runs around at 'just' 60' movement, he is a difficult enemy for foes to handle. He can pop around to appropriate vantage points and get a clear shot on foes. He can track at incredible speeds. When foes with a 60' movement want to attack him in melee in an open space, he can just move away from them 60' and stay out of the range of their charge attacks.
D&D is dominated by melee attacks. If you can stay away from most of your foes and use missile weapons at will, you can do wonderous things ...
Plus, as an added bonus, the fastest guy is usually the first to the treasure ...