I have used both and definitely find that the eggwhite-based icing tastes better - I use the same recipe as Elise87.
The good old Women's weekly
Instead of the meringue powder Malo, have you tried using Pavlova magic instead?
Lemon extract is acidic and has a very high alcohol content - usually around 90%. This is used to: denature egg white proteins so that more hydrogen bonding can occur between protein molecules, thereby stabilizing the mixture, to slightly thin the royal icing without dissolving materials such and fondant or gumpaste with which it may come into contact, and also allows the mixture to dry quickly. You can also use vodka (lower ETOH content) or Everclear - but, the stabilizing effect will not be as pronounced. Besides, lemon extract smells nicer. :-)