The Blast is an "ok" bike, but I think you'll outgrow it quickly. I've only ridden one once, and while it was definitely a light and small bike it just had a "cheap" feel to it. It didn't have the sturdy, heavy feel of a Harley, nor the smoothness of a Honda. The single cylinder 500cc engine puts out about 35hp, which isn't bad but I think you'd get REALLY bored with it inside of a year. But, it would be a great beginner bike so maybe that's a good place to start.
As far as the weight of the bike making it more/less maneuverable, it definitely plays a role in the handling. However, I've found that it has a lot more to do with the location of that weight. If the weight is down low to the ground, even at slow speeds the bike will be easy to turn around. And at high speed, wheelbase, wheel size and suspension are more important that overall weight. A light bike is really nice when you are in the twistys going from one hard corner to the next, but I'm more concerned about stability within the corner and the ability to hold my line. Light bikes frequenty have underbuilt suspension, especially when you look at older bikes under 500cc's. I had a 1969 Honda CB350, and it was a very short and light bike. Tons of fun around town, very "flickable" and easy to throw around tight parking lots and busy traffic. However, the suspension was deplorable when hitting the hills.