I own a Mimiq and Helix. The Mimiq is fantastic, but the Double Take in Helix seems to be just about as good in my opinion. Definitely not worth using WITH the Helix rather than Double Take unless you need to free up DSP and still have a block to run the effects loop with. I use the Mimiq with my HD500x though.
Both sound phasey in mono simply due to what they do. Both can sound like they "jump around" a little in mono. They both automatically change up the delay time which can shift the comb filtering audibly. I haven't used the Mimiq in a while, but I feel like it was a bit better at detecting transients to switch delay settings with, so it sounds a bit more natural. That said, teh difference is pretty minimal.
If you use a stereo mix with in ears/headphones, your going to be very happy with either. I've boxed up the Mimiq and haven't looked back in this case.
However, if you use mono monitoring, or have a stereo rig where the speakers are close to each other (effectively making it mono), I think Mimiq probably wins by a hair.
If you already own one, cool. Do something fun with it. If not, I wouldn't bother purchasing it honestly.