Would having a hard thing stuck to your bat not be more likely to break on impact than a soft thing?
And being stuck to the bat, it it breaks and has no give then the bat will go with it.
Julian Millichamp said a resin toe guard was a bad idea as it took the bat with it, I thought this may be the same
Well it would have to be harder to break than either soft rubber or willow, otherwise there would be no point. And if it requires more force to break than the willow, then any impact that breaks the toeguard would have been strong enough to break the willow if there was no guard anyway. Plus if the guard has broken, it has absorbed energy in breaking that hasn't been transmitted to the willow, good news.
No reason at all why something breaking that is stuck to something else should make the thing it is stuck to break, this just doesnt follow?
A "resin toe guard" could mean different things - if shoe goo kind of affair then of course it won't 'take the bat with it', that would probably imply that breaking the toe guard somehow releases extra energy upon breaking which would then snap the bat. If it means that the toe of the bat has been dipped in resin (and the willow has absorbed some of it), that could change the properties of the willow in that area, perhaps making it more brittle and less able to absorb cricket ball impact without breaking.