"concerned about their lack of instructions as to how to use this die: "after the die contacts the shell holder press down with a minimum of 25 lbs of pressure to force the collet over the case neck".
Okay, I'll try but I really don't have any more to add to the factory instructions, that pretty well covers it. Fact is, it's a "feel" thing that has to be learned. If you know how heavy 25# is, using about that much force on most presses will size most necks quite well.
"Sometimes you felt nothing and other times there seemed to be springing action as the collet was recessed. Well, the die broke as I was starting on the third box of shells."
Well, if you felt nothing, that was much less than 25#! Not sure what you mean about "springing action", the collet has a tappered upper portion that squeezes in on the up stroke and springs back out when ram pressure is released. Normally.
IF you have "broken the die", does that mean you have pushed the threaded soft aluminum top cap out of the die body? If so, you put far too much pressure on the ram! That cap is designed to be a 'safety' device, keeps us from serious damage to the die body or press. Lee is very likely to send you a new cap - and a warning! - if you call or email them.