.....As stated, in those threads, I have found it harder to flick open a knife, and get it open all the way, without a wrist flick, with a thumb hole than without.
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First, a thumb hole is only as deep as the blade is wide. Therefore, you only have as much vertical area to put your thumb against as the blade is thick. Many thumb studs on knives are twice as thick as the blades, giving you more vertical area to put your thumb against.
Secondly, I'm willing to accept that I'm not ably to flick open the blade of my Byrd Meadowlark without a wrist flick because it is a lockback, that has a backspring trying to keep the blade closed. ......whoever else uses thumb holes (who does) make some very good knives with thumb holes on them, I will probably not spend my money on them.