I am about to get a Borla S-Type installed, so same deal as the Atak, meaning I'll have to butcher my stock exhaust.
GTHaus is a great exhaust, but I am convinced I would have used the open mode once every blue moon, and would have been worried about being caught by the plod everytime I go past 2500 RPM in closed mode...
The price difference sealed the decision.
Anyway, back to the issue of cutting the stock pipes: I will most likely need to re-install the stock exhaust for DMV inspections, once after 4 years for a new vehicle, then every 2 years, so I ordered stainless steel clamps like this:
From what I could google on various forums, they make a good connection between same diameter tubes, without crushing the pipes, and they hold well over time, even though in my case it will be a Borla-off / Inspection / Borla-back-on every time, so I don't even need something that holds for that long.
I hope this helps.