Anyone had any experience yet with the new Clarett USB range from Focusrite? I know the Thunderbolt models rate well, but there is little info on the USB ones. My current gen1 18i20 is great, but I was going to move on to the gen 2, but now the Clarett is here, I think the specs would be worth the extra dollars. Any thoughts out there ?

I just got the Clarett 2PreUSB today and hope to hook it up with SONAR X3 Producer tomorrow (running Windows 10 on a new Dell 8920, i7 with Optane). If you're using this or still considering it, please let me know.

The Clarette usb  has good reviews in a recent SOS article. I bought the Scarlette 18i8 and love it. I thought I was getting a Clarette when I bought it. I didn't read the fine print. In my case it wasn't an issue. The latency of the Scarlette is fine for me.
SOS doesn't give good reviews lightly, so based on that and Focusrites track record I personally wouldn't be afraid to give it a shot. 

I have the 2 pre usb.  Really good drivers, low latency (at least with cubase).  Haven't used the inputs, but I'm told they sound *great*.

What you are getting with this model is the same quality Mic Pres that are in the Clarett range. The latency is still fast enough but slightly improved again the thunderbolt range.  The Mic Pres are spec'd a little better than in the Scarlett range.  I have got a Scarlett 18i20 Gen 2 and also the Focusrite Clarett 2 Pre (Thunderbolt) The Clarett is a little nicer for sure. 
 
I recently recorded an orchestra with a pair of quality microphones feeding a Clarett 2 Pre. The quality of the mic pre being one all important thing here. I got a great recording and was pretty surprised how big it all sounded. There was tons of gain still available too. The AIR settings are real nice and add transformer/valve like air to the sound. I am glad I did because the top end was lovely in playback. 
 

Latencywise the clarett USB should be equal to the scarlett 2nd gen.

I replaced my Scarlett 18i20 1st gen with a Clarett 8pre USB and couldn't be happier!!
Sure the Scarlett works great but the Clarett's latency is better, the preamps are great and the AIR feature works great on vocals, bass and acoustic guitars.
My plan is to sell the 18i20 and get a 6i6 2nd gen for live use for it's portability