I have the M11 and I love it. It is heavier than my M8 though. I use Spektrum so the antenna really doesn't help with the balance of holding it. I really like all the adjustment on the radio. You can do as much or as little as you want to do with it. As long as you read the manual so you know exactly what each option does, with all the graph's and stuff, you can get the radio dialed in very easy. The nice big display screen helps that out alot as well.
The Z1 is a very nice radio as well. I will be getting one very soon. Then I really can do a side by side comparison. I have used the KO version of it before and really like it. I just haven't owned one. The KO version uses some different terminology in it so make sure you read the manual. It's not hard to figure out but it's still best to read the manual. The biggest downside of this radio is the size of the screen. It's pretty small compare to the other top end radio's that are out today. The biggest plus to this radio is the feel of the grip and wheel. Very comfortable.