I don't have a lot of experience with leading edge flaps (only tried them once) or canards as they don't fit that well into my flying conditions and flying preferences, but I have tried them, so will relate my experiences. If they are something that interests you to suit your flying style and conditions, there are certainly folks who have written considerably about them on the RC Powers forum, so not to pass the buck, but I would direct you there to start searching for more info if my thoughts don't satisfy your curiosity :).
Where I fly, I have dead calm still days or days with less than 5 mph wind less than 20% of the time. I fly primarily in conditions with winds of 5-10 mph, often up to 15 mph, so having a plane that can handle wind well is pretty important to my flying situation. What I mean here is having a plane that I can still fly relatively smoothly and perform basic aerobatics while it is windy. I suppose I could throw any plane in the sky in these conditions, but I don't like being in a situation where I am basically "surviving" the wind and not having any sort of fun at all. Not a relaxing way to fly and enjoy myself in my experience. As you read through the rest of this post, you will probably realize why I rarely build and fly planes with LE flaps or canards.
Leading edge flaps
When I read posts on the RC Powers forum from those who are big supporters of LE flaps or who design them into their airplanes, essentially my takeaway is that they enhance slow speed flight. I would agree with that, but my experience is that having these fixed flaps on the leading edge narrows the overall flight envelope quite a bit as a sacrifice to enhancing slow speed flight.
Here is what I found was happening. The leading edge flap was causing drag and as speed increased more turbulence and less stability. With KF2 as it got slow, the controls could also get a bit "mushy", not a feeling I like in my park jets. In windy conditions, with those angled flaps, it would get bounced around unexpectedly in a way that was hard to predict and often hard to handle. So I realized for conditions in which I normally fly and my flying preferences, leading edge flaps were not for me.
When the RC Powers Su-27 V5 was first released in Oct 2015, as soon as I saw leading edge flaps, it went on the "I doubt I will ever build this" list for me. However, I continued to follow the thread on the RC Powers forum with mild interest as it was an Su-27 and I hadn't had one of those in my hangar yet. Unfortunately, it got a lot of bad press initially, one of the key things that I saw was that more than one person reported it was a calm wind plane only. Again, this confirmed for me that the leading edge flaps were contributing to problems with how this plane flew and handled the wind. After several months, I noticed that guys were modifying it to fly without the LE flaps with either no KF airfoils or KF4s, so I figured I would give it a try and it has turned out to be just an awesome flying plane.
I have flown three different planes with canards, Su-37, Rafale and the recent RC Powers Eurofighter V5.
However, like about 90% of the rest of the folks who build park jets with canards, I have always had them fixed (ie non-moving). When flying in dead calm to very light wind conditions, they do reduce wing loading, making the plane feel a bit lighter on the sticks and when comparing a Su-37 to a Su-35 (same plane but without canards), the Su-37 does feel smoother in calm wind conditions. I do find the canards slow down pitch and roll performance slightly over non canard planes as they do create drag and resistance in these axes. Additionally, even in calm winds, having that extra lift further forward can contribute to the plane wanting to "zoom" or climb on it's own as speed increases. I found this tendency to be the worst with the Eurofighter V5 as the canards are quite large and quite a bit further forward of the wing than the Su-37 and Rafale.
Bring on the wind and in my experience, planes with canards can start to become a real handful as the wind hits them and really pushes the nose around. Whereas I fly many of my non-canard planes in winds above 10 mph, I rarely fly a canard plane in those conditions, I find they become too unstable, unpredictable and not much fun to fly.
So that essentially sums up my experience with LE flaps and canards, in calm winds they are fine, certainly canard planes look very cool and modern in the air, but what the eye sees and what the wind "sees" are two completely different things in my experience. LE flaps do perhaps improve slow speed handling and stability, but with many things to do with aerodynamics, if you push one part of the flight envelope too far one way, you pay penalties in other ways. So certainly give them a try if they interest you, I would strongly suggest doing your maiden flight with LE flap or canard planes on as calm a day possible before experimenting with any wind. These are just my experiences, perhaps yours will be completely different :).
In the next article, I will discuss KF airfoils, something we have done a lot of testing with in the development of our NAMC planes and I have tested on other designer's planes as well.