Most 3d printers from kickstater have been shipped and released. This project has a basically final design. Kickstarter is always a risk, but projects like these tend to have minimal risk. If you don't have $300 to potentially throw a way, don't but it. But there isn't any complete $300 3d printers of this caliber for sale…
The 15 micron figure is 99% probably the accuracy of the motors, not the endresult. And the 50-350 micron layer will sacrifice X/Y accuracy even more since it needs to melt the resin more to make the layer thinner, but as a tradeoff this makes each 'drop' a larger surface area. So no I don't expect this to be more accurate…