A few years ago I was intrigued by a Mini Cooper S but decided against it. The engines (direct injection) were having problems with oil gunking up the intake valves due to the nature of direct injection; fuel was not washing over the backs of the intake valves, cleaning off the oil. Owners were paying upwards of $800 to have walnut shell blasting done to clean off the crud. One of the remedies explored for that problem was an oil catch can. It was found that it didn't help-not sure why.
deposits on the intakes don't only come from EGR. some come right from the cylinder when the intake valve opens because you don't exhaust 100% of the contents in the cylinder during the exhaust stroke. a catch can can't help with that.