Is this CG-Lock thing actually worth installing on a daily driver?

The short answer is that while it isn't a full safety system replacement, the CG-Lock can absolutely be used on factory belt setups without major modification. It is essentially a mechanical tension assist, so it works fine by engaging with the factory buckle and belt material, which is why it’s seen as more of a supplemental upgrade than a critical component. Nine times out of ten, people who run these things are looking for better lateral support during cornering, which is exactly what the toggle switch addresses.

Regarding the on/off toggle, your intuition is right; it is designed for street use. Most owners who run them casually use the toggle. When you’re just cruising, you want the belt to feel normal and not constantly be under tension. When you pull into the lot for a quick run, you flip it up to lock the lap portion and the belt won't stretch or slide around while you are pushing the car hard. Once you're done, you flip it back off and it releases the tension.

It's not a magic way to stop you from sliding sideways in a severe crash, but for spirited street driving or occasional autocross, it helps keep you centered and minimizes that unwanted lateral shift that makes you feel loose. It makes a difference because the factory belts are meant for general restraint, not high lateral G-load restraint, and that’s where this small clamp helps stabilize you against the seat. The consensus from people who actually run these things is that it's a legitimate upgrade for the Miata crowd looking for more lateral security without committing to a full harness swap.

So, if you are happy with your stock setup otherwise, it’s defintely worth the small investment to see if the added stability during hard corners makes your experiance more enjoyable. Just treat it as an adjustable restraint assist, not a core safety feature.

Ran one in my old CRX for a couple seasons and the toggle thing becomes pure muscle memory fast. On pulling up to the grid, off before the exit road, never had to think about it. Mine came used and the clamp would slowly work itself loose on the buckle, so I kept a stubby flathead screwdriver in the glovebox and gave the mounting screw a quarter turn now and then. A dab of thread locker on that screw fixed it for good.

One thing to keep in mind with a stock reclining seat: the belt tension only pins you in place if the seatback acutally holds you. Mine flexed under hard corners no matter how tight the lap belt was, so I wedged a thin piece of closed-cell foam behind my hips to sit me deeper in the cushion. That combo did more than either thing alone.

One thing I'd flag before you bolt it on: locking the lap portion means your torso becomes the pivot point, so in a hard braking moment before a corner your upper body still loads forward against the shoulder belt while your hips stay planted. I ran a similar setup on a stock seat years ago and the real fix for me was realizing the seat cushion itself was the problem, not the belt. If your stock seat is slick, the lock just makes you fight the seatback instead.

Also worth checking that the clamp doesn't interfere with the buckle's release button travel, since some of them sit right where your thumb needs to go in a hurry.

I'd push back on the idea that clamping the lap belt keeps you centered on a stock seat. Mine just rode up over the sides of my hips every time I loaded it, and the belt doing its job wasn't the issue anyway, it was my backside sliding on the flat cushion underneath me. You end up tensioning a belt against a seat that's allready given up, so the whole thing feels taut but you're still leaning sideways halfway through a run. I pulled mine off after a season and put the money toward a seat with better bolsters instead. On a Miata with factory seats I honestly think that's the better spend.