I invariably use the all silicon Drennan type adaptor and find them very good. I can see where Philip is coming from, but I don't have any problem with making adjustment to depth by either sliding the adaptor up the line or removing the male end from the female for bigger adjustments. If I slide I always use saliva to do so and can honestly say I haven't had a problem in so doing, and this is on 2lb bs line.
Only my opinion, but I find using shot to secure the float more likely, or as likely to damage the line particularly when changing depth many times over a given period, which is what I tend to do when searching for roach at many different levels. I just feel that opening and closing the shot might well cause greater line damage?? We all have our own take on things.....
Regarding the Drennan silicon adaptors; As you know the adaptor 'folds' on the strike. Again in my opinion, and although the actual 'folding' section is mighty thin, I sometimes think it is still too stiff and doesn't fold quickly enough. To this end I am looking at an alternative where the 'folding' section is made from very thin chord (and I mean very thin!) which, on the face of it is far more flexible.
Many years ago (mid 80's) I was given some floats in Korea which had a short plastic peg joined to the base of the float with fine 'chord' and this was truly flexible. The peg was pushed into silicon tubing on the line (just as the Drennan one is) and it worked beautifully. Its downside was the chord had (imho) limited life, BUT it did work very well!!
As I say, I'm experimenting with chord type material and the fixing of it to the actual float and the peg, but this is not a simple matter and may well turn out to be its nemesis......................
Anyway, trials on the cards quite soon!
ps It goes without saying I only use the Drennan adaptors for close in work or a rod or two at most. Any further and I use the 'Crabtree' method..................