profpointy wrote:after all my scepticism....... Mmm...I'd have thought a brown-trouser moment at best would be the outcome with or without the plastic clippy-release. Maybe it's some chance rather than a definite off....
No, once the mudguard starts to crumple (as per the illustration above) it'll almost certainly have you off in the worst way possible unless some kind of QD is fitted. It is a potential killer, pretty much on a par with having your forks break spontaneously.
If you don't want to (or can't) use secu clips for some reason then the danger may be considerably mitigated by using a stay mounting that is set an inch or two above the front axle; should anything get trapped and the mudguard start to crumple, the gap between the mudguard and the wheel will open up (initially) which substantially reduces the risk of a severe jam. I suspect that bike builders knew this exactly in the 1930s (when more fragile lightweight mudguards were first more commonly used) but somehow this was 'forgotten' by bike designers later on. Nearly all quality lightweights from the 1930s onwards for about 30 years had the stay mounts well above the axle, front and rear.
BTW for anyone who has rattly secu-clips; possibly the loop in the stay was deformed (to make it narrower and therefore prone to move and loosen further over time) when the stays were installed originally. In any event if you open up the loop slightly (and then bend the stay elsewhere to make it line up with the mudguard brackets OK) you can make one that was slightly loose snug again. If they are very loose then the (huge.. ) investment in new clips and careful fitting should see you right again.