Thanks, Grant, but this Saffire is FW only.
I'm thinking of getting the MOTU Audio Express, which is FW and USB, so I should be able to use it with any computer.

GjB
(In case you try to use older hardware in Windows 10 via USB sometime..
One thing to consider which has helped me and others with a Focusrite 2i4 (Gen 1), was to only use a USB 2.0 port with Windows 10.
 
It sounds counter intuitive, but since the Creators Update (or a large update like that, (clean ISO install)) the USB 3.0 ports didn't have the same compatibility as the USB 2.0 ports that the older Focusrite hardware was configured for.
So, if you have a USB 2.0 port on your machine or motherboard, try hooking up to that and see if it helps.)

Not meaning to hijack the thread, I have a 1st gen 2i4, just starting to use it and I only have USB 3 in the back but my front has USB 2. I've always thought it best to use the back ports, but in this case, would you recommend my using one of the front 2.0 USB?

robbyk
Not meaning to hijack the thread, I have a 1st gen 2i4, just starting to use it and I only have USB 3 in the back but my front has USB 2. I've always thought it best to use the back ports, but in this case, would you recommend my using one of the front 2.0 USB?

I would use whichever ones you want to use.
But if you get audio dropouts, then try USB 2.0 only.
This is what worked for me and a few other people in Windows 10.
Maybe they fixed the issue. I kept it as it is for now with USB 2.0.
(I actually go straight into the USB 2.0 on the motherboard. My case only has USB 3.0.)

To clear up a couple of things regarding USB:
 
There is no performance advantage connecting a USB-2 unit to a USB-3 port.
 
Prior to Intel Z series motherboards, literally *ALL* USB-3 ports were via 3rd-party controllers (USB-3 hadn't yet been integrated into the Intel chipset).
 
Many older USB devices have issues with 3rd-party USB controllers. 
Liken the situation to using a non-TI chipset Firewire controller with a Firewire audio interface.
 
If you're running a fairly current Intel based machine, you've got Intel USB-3.
This greatly reduces the odds of incompatibility with USB-2 devices.
 
If you've got a USB audio interface that isn't being recognized (when connected to a USB port), that's sometimes caused by an impedance related issue.  Try using a powered USB hub (even though it's typically not recommended) between the audio interface and computer's USB port.  That will resolve the impedance issue, the audio interface will be recognized and work fine.  In this scenario, I wouldn't connect anything else to the USB hub.