I recently bought the Xprotolab, but I am having trouble getting it to connect.  Running Oscilloscope Pro through my 4.3 Nexus 10, I get a "No USB device connected error message.  Thinking Android 4.3 was the issue, I plugged it into my 4.2.2 phone, and I got a "USB device not supported" error message as soon as I plugged it in, and the same "No USB device connected" error message through Oscilloscop Pro.  
The Xprotolab is running the FW 2.22, Oscilloscope Pro runs on anything with Android 3.1 or higher, and I do not have issues with my USB thumb drive through my OTG cable.  I am really excited to get this thing working, so any help will be greatly appreciated.

Hi!, Have you tried contacting the developer of Oscilloscope Pro?

Not yet.  After I discovered that 4.3 does have a bug with USB host mode, I used my phone that runs 4.2.2.  Since my phone does at least recognize that a device has plugged in through USB host mode, I have shifted my focus to it for now, but I get an error message that tells me the USB device is not supported before I even get to the Oscilloscope Pro app.  I also have no problems connecting a USB thumb drive.  So it seems like my issue is just getting my phone to recognize the Xprotolab Portable.  However, I will contact them as soon as I can to see if they have any experience with the issue.

Okay, I finally got it working.  Basically 4.3 has issues with USB support, so I switched my Nexus 10 from 4.3 to 4.2.2, and it works perfectly.  Still not showing up on my HTC One M7 that is running 4.2.2, so it may not be the fix for everyone, but for me, my tablet was my main concern.  Hope this is helpful for anyone in a similar situation.