Too many disadvantages for most players
That said, I guess a disclaimer is in order: I'm in my 11th+ year of using AOII. Being a little selfish, I'd prefer less people use it than more, as it makes it a little more effective when playing pitch games (as it relates to strategy deviations and cover).
If multiple deck games are 1)game of choice or 2)the game most likely to be played, then either Hi lo or KO may be better choices
However, if you'll have ample opportunity for pitch games....then I'd say go for it.
Some caveats: If you don't side count aces....skip it, and learn something else. There's lots of debates on the value of count speed, i.e., SD countdown, DD countdown etc.. Some feel it's ok to count down decks slower as you won't lose much.
Here are my thoughts on this....
Why play pitch, use AOII, add ace side count, and not go for the gold? In other words, it takes less of a bank, lower variance, lower spread to play a winning SD game than any other. You want to be able to continue to play and it will already be difficult enough if you bet multiple green, black or higher. You will be highly scrutinized, and you better be able to talk and count at the same time. To facilitate this you must be able to count down decks with blazing speed, and be accurate with your TC conversions, as the main advantage is in your play variations. For TC use 1/4 deck estimates for DD and SD. (Quick TC conversions can made by multiplying as well as dividing, e.g.; 1 3/4 decks use X.9; 1 1/2D use 3/4 -X.7, whichever is easier for you, 1 1/4d use X.6, 3/4d use X1.3, 1/2d use X2, and 1/4d use x4.
15 sec for SD is a must. DD is a max of 45, but 35-37 sec is what you should get consistently. Needless to say, accuracy at fast speeds is paramount. There are many other skills necessary to play SD successfully (DD is a little more forgiving).
There is another consideration before you decide to invest the kind of time required to make AOII or Hi OptII work for you, and that's whether joining a team is in your future. If it is, and unless you already know potential teammates who use level 2 counts, then you may be wasting your time. Most teams use level 1 for counting, and of course for tracking.
good luck
cheers
bfb