The older 1 was far to soft IMO,the stiffness of the brushes in the newer 1`s are much superior.
Absolutely, the first brush didn't have enough scrubbing power, the new one was to my delight much better.
The only ones I would use the softer SL brush on, is for newer leaded windows, and deep recessed georgian panes. The mark 2 can sometimes be hard in that work.
But it's the perfect brush, in fact, I never ever change brush anymore. Hence it saves time, and earns more. It's amazing how insignificant £45 for a brush is, when it can earn you 1000x that or more! (Brushes seem to last quite long)