I've got three Kicks and a Sigelei clone. I've really enjoyed my Kicks, and I got the clone just to see how it compares. I've had similar observations to those of RPad. The clone won't fit in my GGTS -- the Kick will, but it's tight. It also won't fit in my Super-T Kicklet, which is what I got it for. I don't own any of the Sigelei mechs, but the only device I've been able to use it in is my Kick edition Jazz Cartopipe.
The plastic sleeve on the Kick is an advantage over the clone, because there's less stuff that can get hung up on threading, and therefor the Kick is less likely to be damaged or get stuck.
The clone does indeed make a whirring noise when it fires. It's audible over the delivery systems I use, except maybe for crackly cartos. I'm assuming that this is the module sending pulses to continuously check the ohms of the attached device. I find it kind of annoying, but it's not a dealbreaker or anything like that. The Kick does something similar, but it's only audible when the battery is absolutely dead, nothing is firing, and you have your ear up to it.
I absolutely agree that the Kick's low-battery warning (a series of short, intermittent fires in succession) is an advantage over the clone, which just stops working when it dies. I didn't fully appreciate the Kick's warning system until the battery went low the first time I used the clone. I had no way of knowing if I had a short, had popped a coil, or if the battery had died.
I think the Kick's negative contact spring is also an advantage over the little negative contact on the clone. The spring on the Kick can be stretched to make contact if necessary, and I wonder how much wear and tear the clone's negative contact will take before the solder pops off.
I'm glad I only paid $15 for my clone. It's a bargain at that price. It's not a bad device and it seems to perform just fine, but at full price, I'd gladly pay the extra money for a genuine Kick.