If you're just talking linear VCAs, it's one of the better space-saving choices. However, I would be more inclined to look at something which offers more flexibility even if this means taking up more space. Take the Intellijel Quad VCA, for example...in that case, you get four VCAs which can also sum down to allow the module to function as a mixer, adjustable behavior between linear and exponential (which tends to be better for audio signals, because of how we perceive loudness), a signal boost per VCA, and so on. Granted, the Intellijel is 8 hp instead of two and costs $100 more, but I feel that you get more functionalty that justifies the price difference and extra width use. Since your current layout is lacking in a multisource mixer and VCAs, better to kill two birds with one stone here...and then some, really.