IMO, vertical play and wobble are entirely different animals.
Blade wobble, for me, is most often associated with peened pivot traditionals regardless of whether they are slip joints or lock backs. There's simply a limit to the amount of lateral stress this design can sustain without developing wobble. Wobble doesn't matter too much to me because it is so easily fixed with a padded vice. Heck... I've even taken the wobble out of several Swinden key knives. I just clamp 'em down with enough force that I'll either fix it or just bust it to pieces.
Vertical play is a reality with every traditional lock back that I've used, no matter what brand. As I understand the phenomena, there are 2 technical issues. The first and most obvious is the stability of the blade pivot pin and the lock bar pivot pin, both of which see significant forces under hard cutting. Several knife mechanics (I'm *NOT* one) have told me that their standard fix for vertical play is to replace these pivots. The worst knives I've owned in this regard were two Bucklite Max folders, both of which developed significant vertical play in less than a year. I sent them to Joe Houser and he confirmed to me in email that the plastic liner-less designs are simply weaker in this regard, as the frame material opens up allowing the pivots to move. The other Buck that was really bad in this regard was a Walmart Spitfire (I forget the exact model name). The pivot assembly visibly moved in the frame. That appeared to me to be a production QC problem with tolerances and I hope Buck works the kinks out, as I sort of like that knife.
The second and less obvious issue with vertical play is what happens at the blade tang/lock bar interface. To allow the lock bar to move into position, typically this interface has a slight angle. Under hard cutting pressure, the blade tang literally forces the lock bar up. You can feel this on most lock backs if you keep your thumb on the lockbar under hard cutting. IMO, this sort of "lock rock" is inherent with the lock back design but some are better or worse than others in this regard.
IMO, there is a real safety issue. I've heard many reports of people having lock backs accidentally closing on them when using the knife to cut limbs or tough rope. In all the reports that I've heard or read, the failure mode is the same. The user was cutting with an extreme amount of force and when the blade finally cut through the material, the blade snapped shut on their hand on the sudden follow through.
My understanding of this failure mode is that the hard cutting force lifts up the lock bar enough that the lock bar pawl no longer is in position to catch the blade. Then, when the blade breaks through the material suddenly, it snaps forward like a sling-shot and does so faster than the spring of the lock bar can recover.
I think the lock back design is fine for EDC and hunting uses. I don't think it's the best for applications (like brush cutting) that create this sort of hard cut & release scenario. If I'm clearing brush, I'll reach for an Opinel over any lock back, as the Opinel's lock ring design is pretty much impervious to developing vertical (or horizontal) play. (It has other weaknesses though, which is why I prefer a lock back for hunting.)
As much as I dislike Cold Steel (really, they make WWE look civilized), the Triad lock design fixes a real design weakness in the lock back design.
