Seems like people are very divided about this.

Some say they're very good because you can buy it and keep it for years while 125 will feel boring after a month and 300-500 will feel boring after a few months.

Their opponents say that SV650 is even less beginner friendly than a 600 supersport because it has just as much torque, less "smooth" engine and worse handling. Instead they recommend 125 as the first bike.

Others are in between. They consider 650 a bit too risky and recommend 300-500 as the first bike.