this is just my opinion,
as i have been wearing these mixes for a few years now.
IS/A is a synergy.
it was well thought out, tested,and found to work exceptionally well with this recipe that is TAL dominant.
MX135 is a synergy as well; it is a TAH dominant mix and works as well as it does because the recipe is perfect.
using 2 mixes basically changes the whole recipe.
the balance of whats dominant is totally thrown off and you end up sending a bunch of signals that overwhelm those around you.
i think alot of people here think using 2 application points makes a big difference.
honestly, if i appy one to my wrists and then one to my hair, im basically still within inches of both app points and i am overwhelmed myself 
simply put, if you want a great dinner and then a satisfying dessert, it is not better to just throw them both in the same mixing bowl because they are going to end up in the same place 
I personally never mix MX135 and IS/a or B together ever.
they are just so perfect on their own that more is definatley not better.
the only exception to this rule is that i do have separate bottles of TAH and TAL, and occasionally i will use more TAH in a TAH dominant recipe, and more TAL in a TAL dominant recipe.
also, i use instant honesty with both, and i agree this also changes the recipe, but only in favor of verbal reaction for me, and i cant speak on behalf of anyone else here.
i can say however that i was having a bad night wearing MX135 one time and it was only because i was working and the TAH wasnt helping with tips.
i knew IS/A was already good for tips, and i tried to “save” my night spraying IS/A over the MX135.
needless to say, i wont be wasting my precious mixes that way again.
the night ended and i wasnt any richer for it.
i wear MX135 or IS/B out and about, and IS/A is definatly my money maker / husband-grabber.
::sniffle::
i just love them both so much !
hope this helped…