I've read that VRM box could add up to 20 ms additional latency. Since it is a mixing tool, I guess that isn't a problem in most cases.
But they have discontinued all VRM related products (even the Saffire 24 Pro DSP), so I was unable to buy a new one. The Saffire 24 Pro DSP actually does the processing on the interface so I was interested in getting that.
Instead I settled on the TB Isone VST plugin. But people that A/B'd both says VRM box is better than TB Isone. At least it doesn't add any additional latency and was only $20 IIRC, so there is that.