I have built 2 KR2, and was always dead set against flaps or speed brake ( belly board ) because I considered them to only add complexity and weight to the KR. However, after reading all the glowing remarks on the belly board, and having to slip to a landing almost every time, I decided to give it a shot on the Black Bird. The installation is documented on my web site. I can assure you that it would have been much easier to do if I were not so stubborn and had done it while building. I don't know how well the flaps work, but some added lift would be a good thing, if they could provide it.
Bottom line, I would not build a KR without one or the other. The speed brake improved the visibility on landing so much that I use it at full deployment on every landing. The KR slips very well, but for me, it was always a break in the procedure and made alignment with the runway very difficult. I could not establish a procedure for landing. The speed brake solved that. I built mine using aluminum to keep it thin, but because of the weight I am considering replacing the aluminum with carbon fiber. I just need to figure out how thick I need to make the board to give me the same rigidity as the aluminum. I deploy mine at 80 mph, but could probably deploy it at higher speeds if there were a reason to do so. See N64KR at http://KRBuilder.org - Then click on the pics See you at the 2012 - KR Gathering in Mt. Vernon, Il MVN 40th Anniversary There is a time for building and it is over. Daniel R. Heath - Lexington, SC http://www.krbuilder.org/MyUSA/
