A CAS transit is something that many people make a big fuss over, when in reality there is nothing to it. Follow the local procedures, do what the controller tells you (as long as it's safe), follow/report at the VRPs as instructed and don't get in the way of landing/departing traffic. If it's too busy then the controller will decline transit; go around it.
I don't think you are more or less likely to receive a transit whether you are VFR or IFR. It usually is purely based on how busy the CAS is.
In response to a previous poster I don't think ATC keeps a "black book" of unsavoury characters. However what does cheese them off somewhat is prats who don't have a clue what they are doing and fanny about in the busy CAS, e.g. folks who don't have a clue about CAS transit/local procedures, bad RT, people who request transits that take them through ILSs, people who don't follow VRPs/entry-exit lanes etc.
Smithy