What do you guys think, in comparison to Apogee Quartet or Focusrite Clarett?

Nobody?

The Clarett (last time I checked) was still Mac only.
I've heard they're developing Windows Thunderbolt drivers.
 
Apogee Quartet is Mac only
 
The Antelope Zen Tour is Mac and PC.
 
Thus, the reason you're not getting any response.  

Cheers Jim !

I would take a look at the Gearslutz pages if you are interested in Antelope.... Not much love... 

I have been using this for about a month , Amazing! Have the Mr816 as well so that is my comparison.
Effects are super , pre's are a step up from the MR818 which are very good as well .
Routing is just crazy in what you can do .
As far as gearslutz , your have someone upset about not upgrading the Zen Studio causing most of the complaining. Of course I a biased :)

David
I have been using this for about a month , Amazing! Have the Mr816 as well so that is my comparison.
Effects are super , pre's are a step up from the MR818 which are very good as well .
Routing is just crazy in what you can do .
As far as gearslutz , your have someone upset about not upgrading the Zen Studio causing most of the complaining. Of course I a biased :)

Yea, the boys over there are really going at it. I say use what works and make music. While I would like gear to be supported forever I don't expect it to be. Time marches on and the technology only gets better.  

Went over to Gearslutz. Indeed, just some Zen Studio guys who would like to have what the new Zen Tour has. Which in fact means that Antelope should have made a worse Zen Tour.
Well, things evolve and the future is now. Glad I checked this Zen Tour out. Ordered yesterday.
And today I found this:
Future Music Autumn 2016 issue bestows its Platinum Award upon the Zen Tour (9.5/10).
"If you want a high-quality interface for studio, rehearsals and gigs you have to look at this. And their online support is excellent."
Conclusion:
"Antelope have a very good reputation for sonic quality and the Zen is no exception. It stands up very well against the other interfaces in my studio but it is its incredible flexibility which is the real winner. You can set up two headphone balances and a monitor mix all with zero latency monitoring even if using onboard DSP, it makes re-amping a doddle, happily handles 16 extra channels via ADAT and fits in your computer bag along with your laptop. It holds its own sonically with pretty much anything on the market. Excellent."