I think it may be confusing to some. I think 'zed' can be easily misunderstood for zero, and that's pretty much like another way of saying aromantic.
Also, if zed was choosen because its on the other end of the alphabeth, that's another can of worms. Other sexualities and romatic orientations are not the opposite of 'a', because that's just not it. Zed to me kind of suggests that its an extreme, its just too all-or-nothing.
There will be people who dislike the term because of some reason, but these words were not really meant for them. They were created by a minority, to talk about minority issues.
As @Zemaddog said, people are pissed off because trans people, aro people and ace people rant online, and they took it personally.
What they don't realise is that no matter how many trans activists post a very mean image with a pastel background that says 'down with the cis', these people will not have and have never had any power to discriminate against cis people. You don't get beat up because you are cis. You don't loose your job, your family, your friends... They aren't saying f.ck the individual people who are happy with the gender they were assigned at birth. They are saying f.ck the concept of being cis, this pressure to live your life a certain way, and the consequences you have to face when you do not conform to the norm. Also the mindless, oblivious herd that maintains amatonormativity, allonormativity, transphobia, racism, etc. without even questioning it.
I choose to use these words also to show solidarity, and to empower these groups. It can be way of saying that I'm aware of my privilege, and I don't expect all people to be like me. By normalising the use of these words, we also normalise the people who created them. In a world where it normal that your blogs says that you are cis, its not taken for granted, maybe trans kids will feel more normal when they choose to be visible. Maybe this way trans people, ace people, aro people will find each other more easily online.