Back in the mid seventies I purchased my dream sound system: Teac-3340 four channel 1/4' tape reel-to-reel that handled 7" or 15" reels at 15 or 30 inches per second (ips) recording speed, the companion eight input \ four channel mixer, companion Teac AN-30 four channel Dolby A/B noise reduction system, Panasonic two \ four channel eight track recorder \ player, JVC two channel \ quadraphonic turntable with two cartridges and cartridge heads (one stereo and one CD-4), Sony TC-730 stereo tape recorder with built-in sound-on-sound and echo, Pioneer QX-949 four channel receiver and four Pioneer floor speakers.
 
I saved every penny I could while in military service and ordered the equipment about a month before returning to the US from an extended tour of Southeast Asia.  The package cost a little more than $2,500 in 1975 US dollars and arrived at the post office one week before I returned home.  Two trips to the post office in a pickup truck and later a U-Haul trailer rental to take from my Dad's home to my next duty station.

Back in the day I had a Roland VS 880, a very slow AMD  computer,and Aardvark interface, an Alesis HR-16 and a Korg M-1. That was basically my setup. I was using bookshelf speakers for monitors through a consumer stereo amp and recording to cassette.I guess I don't miss those days compared to the tools I have now. I still use a Mackie mixer in my studio sometimes. It mostly gathers dust now though.
 
The main drawback for me concerning a few of these new mixers is the usb only captures the master buss. That's a deal killer for anyone who wants a good take of each individual track. With Zed, it's like they simply decided to tack on a cheap recording solution. Pretty much useless to me. 

Yeah, it's too bad. They were so close to making the ZED mixers truly awesome. They dropped the ball big time.

It's one of those "you get what you pay for" situations. 
The under $500 mixers that sport USB will only be stereo in/out USB.  usually the highest channel can be swapped between RCA/1/4" or USB. 
 
I have a Soundcraft Signature 10 that is like that and the stereo USB channel was what I needed  for playback from my laptop of backing tracks. Otherwise you have to go to the bother and extra cables of an audio interface or ( shudder) use the 1/8" jack. One more thing to go wrong. So far this board has performed beyond my expectations and was money well spent. 
https://www.soundcraft.com/en/products/signature-10
 
If I played in a bigger group I would for sure get a mixer that could multitrack as I'm one to record just about every gig I play at. Once again the Soundcraft was high on my list. 
https://www.soundcraft.com/en/products/signature-12-mtk
 
 But looking now at the Tascam in the OP,, I think I would go that route. All my Tascam gear has been a bargain. I am still using my Tascam us1641 since they updated the drivers a few years ago I see no reason to upgrade. It has better performance and stability than my Scarlett 6i6. 

There was a discussion of the XR18 usage in Sonar here on the forum:
[http://forum.cakewalk.com/Anyone-using-the-Beringher-Xair18-m3505035.aspx ]
 
In general the multi-channel recording is solid through USB, but the round-trip latency is too high for input monitoring.  Since this is a mixer, you should be able to arrange for mixer-centric monitoring and avoid round-tripping through the software.   
 
Soft-synths are always the bugaboo, so managing the way you use them is the key to success.  I use an M32 that shares the relatively high latency of the XR18, but I've managed to keep soft-synth sound generation confined to another computer, and therefore I'm free to leverage the many strengths of a mixer as an interface.

I've had two sub $500 Behringer mixers that had USB on them (still using one of them), and the latency is so bad it isn't worth messing with. Sounds no better than the 1/4" or XLR outs anyway. At least I can't tell the difference. That's why I've hung onto my old Echo MIA card all these years. USB just doesn't seem worth the effort.
 
Bill