Our SimonK ESC's have been out of stock for about 1 month now due to some supply issues with our manufacturing partner, but fortunately they have now all been resolved and are back in stock.
We also have more stock of our 20A, and 30A quattro ESC which is great if you are looking to build a quadcopter and dont want to mess around with soldering a PDB together. Other advantages of a 4in1 esc is that it includes only 1 BEC (voltage regulator to ouput 5V to power your flight controller or RC gear), the 4in1 ESC also inlcude a large single heatsync to keep the ESC's running cooler than individual ones especialy when its buried deep inside your quadcopter. The other nifty feature of the 4in1 quattro ESC is they are compatible with the USBlink device to change settings easily via USB on your PC.
Lastly I can also suggest you add our new 8 way ESC hub to make calibrating your ESC's much easier