Vacuum is the only way a distributor has of knowing how much load there is on the engine, so it can add advance not just with revs but also load. Don't go for the non-vacuum 123, you might as well stay with a 009. I've used the 123VW-4-R-V for several years on a Type 4 engine with IDFs, it works fine. I purchased it from Classic Auto Elec in France – not much use for you but it was the best deal I could find at the time. If you like fiddling the 123 tune gives you the opportunity to optimise the ignition map for a particular engine under particular conditions. And apparently it can tell you the time, how hot it is etc. just by looking at a mobile 'phone. I believe it can also immobilise the engine, and that feature alone would be enough to make me avoid it.