Personally I hate any kind of "Mat" heating system. I prefer using cable so I can get a more even heat and heat the entire space.
I find that walking off the matt to the no heated tile feels weird under foot.
I have had multiple complaints from men who have cold feet when they pee and women who have cold toes when they get ready at the mirror. No we cable heat.
I like the NuHEat system with their newly designed wire cleats.
We have done a ton of installs with Warm Wire and it's a great wire but the install cleats troublesome.
The system from Flextherm looks Hogee - I don't like all the plastic square pieces.
Never used Suntouch so I can not say.