This puzzle is by far the best square-1 on the market: it has smooth and fast turning, and best of all, it cuts corners, making lock ups occur significantly less than on other square-1s. Despite its speed, it's controllable enough that algs can be executed fluidly.
However, it's not perfect, and modifications are still necessary if you want to maximize this cube's potential. It's not completely stable, so you may have to glue certain pieces to the core to fix this issue. Furthermore, some of the edges pop up occasionally, which is annoying during solves. It's not anything like a pop, but you do have to push them back down in the middle of the solve, which obviously slows down your times.
Nonetheless, this is still by far the best square-1 out right now, and it is the only one I recommend to anybody purchasing a square-1. There's no reason to get any other square-1 over this one.