These aren't for everyone, especially people with shoulder issues, but if your shoulders can handle them you'd be hard pressed to find an exercise that fries the pecs like ring flyes do. And you can make them harder by setting the blast straps wider.
Be warned though, regular ring flyes with the blast straps at shoulder-width are tough enough as it is, but setting the blast straps wider makes them downright brutal. As a point of reference, several months ago I could do regular flyes with my feet elevated and a 50-pound weighted vest for sets of 8-10, but couldn't even do one full rep with the blast straps wider unless I did them from my knees – and even that was a struggle.
With practice I can now do 6-8 unweighted wide flyes with my feet on the floor when I'm fresh, but if it's at the end of the workout, I can't even do one. So if I do them at the end, I'll do them on my knees, which is still an awesome finisher.