My MX-7-180 handles much better landing with vortex generators than without. I had them installed in 2010 by Maule Flight when they rebuilt my airplane. Before the vortex generators, the airplane would suddenly stop flying and plop onto the surface. With the vortex generators it continues to have lift and control all the way to touchdown as well as a lower stall speed. There doesn't seem to be any speed penalty in cruise but my 31" bush wheels create so much drag that I wouldn't notice.
According to Micro Aerodynamics'
website the reason that the airplane handles so much better at low airspeeds is that when a stall starts at the wing root and tries to move toward the wing tip, the vortices inhibit it's progression so I have lift longer. With full flaps they say that the vortex generators lower stall speed about 4% to 43 mph but I've found that they actually lower it more than that. I did stalls in all flap settings at altitude when I was in McCall ID. With 48 degrees it stalled around 35 mph but the airspeed indicator isn't accurate at that low an airspeed.
I'm much more comfortable landing at a lower final approach airspeed (55 mph) with the vortex generators so that opens up shorter airstrips. Now I have to worry about landing and not being able to take off again with the 180 hp engine so I use a takeoff and landing distance estimate of 500 feet unless the landing zone is uphill.