I received X4 (H107L) from Holy Stone Predator (HS170). Same engines, same size, same upper hull, but a completely different feeling in flight. While both are very funny for their own reasons, the more I fly the X4, the less I fly the Predator. X4 appears to have a higher overall skill cap. Jerky and responsive but can also crash if you flip the controls too quickly, that's not a complaint, it just means you have better control and shouldn't pull too fast which will crash! It's a lot less manual and requires you to be more respectful of the controls (especially those with high sensitivities). You can adjust the sensitivity for rudder (yaw), aileron (left and right), and elevator (forward and reverse). The transmitter saves your sensitivity settings. It also remembers your trim settings, so you don't have to do this every time you start the quad, which is a nice touch. With high sensitivity, the aircraft will be more powerful but also more sensitive. Yaw can be cranked insanely high, so if you need fast yaw then you'll love this quad. I personally keep the yaw angle at 75 and the other two settings at 100. The transmitter is very good, there is almost no "dead zone" for rudder, aileron or elevator. This gives you very good control, he doesn't do anything and then suddenly moves too fast. Giving the right stick a little nudge will hardly move it in the right direction, same goes for yaw. The same is not true for the Predator, which has this problem with the correct stick for the aileron and elevator. Spare parts are cheap. If you are not afraid to screw up the engine, you have the opportunity to learn a new skill and start soldering. If you decide to buy the X4, I recommend you use Holy Stone Predator (HS170) props. They're a bit bigger, giving you a bit more power, wind stability, and a bit better battery life. I think Hubsan should equip the X4 with these props right away. If Hubsan is reading this I will ask them to try these screws on the X4 and see for themselves.