Drawbacks: Ash is opened grained like oak so is hard to fill grain to make a smoother shaft. If you do fill the grain with finish, as our English friend suggests, there will be drag on your closed bridge from this finish. Snooker players use an open bridge so this doesn't bother them. Closed bridge players need a glove or copious amounts of Talc.The dark grain lines distract many players attention while aiming. Ash makes for a stiffer hit than Maple which some players may not be comfortable with.
On the plus side. Ash is stiffer than Maple when the same taper is used which can be a benefit for some players.
Summary: Ash is great if you use an open bridge and want a stiffer hit with your present taper and the prominent grain pattern doesn't bother you or if you want to use an extremely small shaft such as 8 to 10 MM. Otherwise, Maple is hard to beat.
Dick