You don't get the same xp from a knowledge vs combo elixir. They both increase your xp gains by the same amount, HOWEVER, the combo has a travel lix so you can run to the next mob 60% faster than with a knowledge. The combo increases your base health and energy, plus it regenerates health and energy. The combo gives you haste, so you attack and kill faster. The combo increases your armor and defence, so you take less damage and can go from kill to kill. All of these combine to give you faster and more kills, resulting in more xp in the same 15 minute life of an elixir.I think you guys are meaning bang for your buck. You get just as much xp from an xp lix as a combo.
So for some, it will be more cost effective to use a combo or for some xp and haste.
My opinion is only for me with 5k+ hp, 800 def, almost 1k light heal, and full dl aura, and near maxed evasions along with almost 300 regen per tick.
If someone has a lot of regens, ring of swiftness for 30% travel speed increase, a Druid to heal them, armor with stat bonuses, then they probably don't need to spend the extra gold on combos.
You need to re-read the second post on this thread. The OP is asking which elixir to use, and Curry tells him a knowledge and haste lix gives MORE xp than a combo. That is a false statement. You keep saying that you get the same xp from either elixir, and that too is false. Combos cost a lot more then knowledge elixirs. If you could get the same amount of xp from either of those, no one would buy combos since they could buy twice the number of knowledge elixirs for the same amount of gold, and level twice as far.