I use Würth because it comes in a pressure pack rather than a tube, but its all the same stuff. You don't actually need much, I used about 100-150ml to do a full Lotus front clam which was a big 4 piece mould. 

I guess if in doubt, more is more, but the more you apply the bigger the clean up job so really you just want enough to seal the flanges. If your flanges are flat and straight then its easy, a thin bead (I do two beads, one along the top of the flange and another along the bottom, as well as a circle around each bolt hole) is enough. If your flange goes around corners or is a bit rough then you might need a bit extra to seal it up. Just watch for it squeezing out the top onto your mould surface, have a clean rag on hand to wipe any of that away.

Be aware it doesn't work every time, I would say its about 90% successful. I feel the times it isn't successful is when I have to drag the flanges across each other to get the bolt holes to line up and then it disturbs the silicone and creates an air channel. A few times it can still be sealed by smearing some extra silicone over the joint on the outside of the flanges, as well as over and around your nuts and bolts. Sometimes it just doesn't seal, and in these cases it is very difficult to know if it is actually leaking through the mould or whether you have a leak in the bag/bagging tape. This is when I would double bag and place the entire thing in an envelope bag.