With the exceptions listed above, nobody lands the aircraft in the crab. Every aircraft is landed pointing down the runway with the wing into wind either down or about to go down as the aircraft touches the runway.
So, the only difference between the two methods is how early the nose of the aircraft is aligned with the runway centerline.
In the "crab" method, this is in the flare and in the "wing low" method this is some time before this.
Students (and PPLs) can often have hard enough of a time getting the flare right. Adding in the transition from crab to wing low at this critical time can produce overload.
Word of Warning. When flying wing low the ball is way out to one side. If you get slow and stall, the aircraft will spin. Flying with the ball way out to one side causes extra drag. Thus in order to prevent speed decreasing, one needs to used an increased power setting.
The above warning is something to be aware of. So if flying wing down, add a knot or two and dont reduce the power too early.
My recomendation is to set up the aircraft on final approach not below 500ft crabbing into wind. At say 300ft, adopt the wing down method and fly the aircraft down to the flare. Remember that as power is reduced, speed will decrease more rapidly than normal and with this decrease in speed comes a requirement to increase control deflection in order to keep straight.
As experience and confidence increases, move the point at which the changeover occurs closer and closer until you are making the changover in the flare.
Personally, I still fly wing low from about 200ft because I find it easier.......if the rudder isnt enough to keep you straight then there is no point in landing because you will end up running off the edge.
DFC