If the knife is intended for utility use and "last step for defense" - I would advise to give up with CRKT Kasper. This knife is designed for fight, in my opinion it is by far too heavy to daily carry. Not last issue - it
looks like fighting knife and this look can make you unwanted "advertising".
Now let's compare CRKT M16 series and SPYDERCO Endura.
In my opinion steel is not issue here, the difference in edge holding between ATS-55 and AUS-8 might be quite unnoticeable in real life.
M16's are stiffer and stronger, especially the series with aluminum handles.
Endura has by far slimmer and lighter package.
M16's are designed for tip-down carry.
Endura (or Delica if you want smaller knife) are designed for tip-up carry.
M16's have liner locks, Endura (Delica) are designed as lockbacks.
Blade shapes differ a lot also. Prices are quite comparable.
So think about your personal preferences in these matters and make your choice.
Quite important - try to handle each knife and decide which fits your hand better and allows more comfortable work. Think this is much more important for knife daily use than steel, locking mechanism design etc. - just my opinion
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Sergiusz Mitin
gunwriter
Lodz, Poland