Here's a test you might try ... get the biggest meanest guy you know. If you know a guy who weighs 230 pounds and is full of prison tatoos, that's perfect. Now, have him act angry, like he's about to charge you. Keep in mind if he gets to you he'll probably not just punch your face, but through it! This is life-threatening -- you stop him fast, or die (otherwise, you wouldn't be justified to use the knife). Hold the spin in your hand ... feel confident that you'll put him down fast with it? I'm not asking if you're confident you can put a big ugly slash in him; I'm asking if you can do enough damage to STOP HIS CHARGING ATTACK before he pulls you apart. Is the Spin still your baby?
Now, if you have the bucks, dull one of your Spins into a training drone, and attach the lanyard as you suggested. Clip it to your pocket, as it will likely be at the beginning of a real criminal assault. Have your aforementioned friend "attack" you, just using controlled punches, and you spend 20 seconds blocking him and grappling him (do this as a drill, he shouldn't really hit you hard or take you down, I just want you putting forth a lot of energy dealing with him). What I want is for you to have your heart thumping, as it would be in a real criminal assault, before what's coming up next: you will disengage from the big guy, make about 5 feet of space ... but here's the rule, as soon as you make the space and start grabbing for your knife, he's going to charge you, and if you don't get that knife out and jab him with it, he gets to thump you in the chest. Did you manage to get that little handle and lanyard positioned right in your hand in time?
What I"m trying to do, of course, is raise the stakes a bit by introducing some reality. When you're in your living room, casually putting the knife in your hand, it may feel secure with the 2-fingered grip plus the lanyard. But during a panic draw, when your heart is thumping so your minor muscle coordination is compromised and you're scared because your training partner is going to thump you if you DON'T GET THE KNIFE OUT RIGHT THIS VERY SECOND, that's another thing entirely . And if having your big partner charging you is scary, up that feeilng by 10 when it's a real-live bad guy who really wants to hurt you. That's a reason many of us want big secure handles and the most optimizied ease-of-draw possible. We also want stopping power ... the ability to stop a criminal assault, where failure to stop the assault very quickly could mean you or your loved ones could die. Stopping him is the key ... cutting him doesn't help if he doesn't respond to the cut until after he's killed you and your daughter, right?
I'm not saying that if all you have is the Spin, you don't use it. I'm saying, though, that you shouldn't significantly decrease ease-of-draw, security, and stopping power for some theoretical marginal legal advantage, if you're truly talking about surviving a life-threatening criminal assault.