Haro doesn't have any flatlanders on the team and does not make any true flatland specific bikes. The M6 is a good dual-purpose bike, but not a really good flatland only bike. Or, more accurately, if you are only going to ride flatland, then there are better bikes for the money for sure.
The Hoffman Momentum PL1 for example is one of the best complete bikes on the market using top notch components. The Ares completes are also 100% rider input designed with a focus specifically on flatland. They aren't built to handle street, they are built for flatland, and flatland only.
The Haros are good, but just not the best if flatland is specifically what you are looking to do. I have spoken with Haro about this and they are very insistent that they want the Master to remain 'dual-purpose' and not flatland specific.