Just used it in changing the front sprocket on a '12 Ninja 1000.
The "Jammer" wedges right in between the chain and sprocket, and works great in keeping the chain drive from rotating.
In the past, I would have to hold the rear brake pedal down while loosening the drive sprocket nut. Often times this wasn't enough (especially if I was loosening the drive sprocket nut), as the torque needed to break the nut loose would overpower the rear brake. With the Jammer in place, I no longer have this problem, as it locks the drive in place without any issues.
If using a ratchet drive (tightening or loosening), you will still want to hold the front drive sprocket with your hand, as the "Jammer" only keeps the drive from moving in one direction. This is particularly important if you have the Jammer placed between the top of the chain and the rear drive sprocket (to keep the drive from rotating clockwise). When turning the ratchet back counter- clockwise, it might release tension on the Jammer, (as happened to me) and rotate the drive enough to let the Jammer fall out of place. Wasn't really an issue for me, as holding the sprocket does resolve the problem; but it sure was annoying to have to stop and look for where the Jammer fell.
The only negative that I found using the Jammer, is that there was some small maring of the finish in one spot (forward of the teeth (chain side)). It's very minor, and dosn't really affect the continued usability or function of the tool, but it does reflect that the tool is made out of aluminum and can be damaged if not careful. To be honest, I'm not really worried about this, as I would rather have the tool be damaged than the new chain.
Great for ensuring the whole wheel assembly is pulled firmly against adjuster blocks/bolts when finishing up a wheel change or chain slack adjustment. Pushing/kicking the rear wheel against the blocks works if you ride a KLR, but for more exacting bikes this is a great tool. When tensioning rear axle bolt, this is inserted between sprocket and chain to pull the rear wheel forward, keeping chain alignment as adjusted.