I used Vetterman's exhaust on my RV6 and at 900 hrs never had a problem with the joints. He also adds other slip joints that allow expansion & contraction in the system.
The only problem I ever had was at about 750 hrs, I got a crack at the flange on cylinder 1. Veterman made me a new pipe piece which ended up costing me about $60 for the new piece and shipping.
Not too bad if you ask me.
I'm building an RV8 now and I have another new Vetterman exhaust for it.