I had an Agency Power on my E93, which should be the same exhaust as the Megan brand. Overall, I loved the sound of the exhaust, but my wife thought it was too loud, so I switched to the OEM mod.
You can mount this exhaust, but as the OEM exhaust has a "channel" formed to accommodate the rear projecting part of the brace, modification to the brace is required.
For my install, we cut the portion of the brace that would interfere and painted the cut end to prevent rust. The brace needs to be re-mounted to secure the other bracing under the car. I noticed no change in handling, as the rear brace is more likely there for rear crash absorption.
I bough a new brace (about $90.00) when I reverted back to OEM. I still have my modified brace, so if anyone wishes to go this route, just let me know and perhaps we can work something out and save you the effort to cut the brace and then buying a replacement, if you ever want to go back to stock. Use my cut brace, keep your original one on hand.
I was not really concerned with the cut brace on the car and know that others have done it. I figured that since I was going back to stock, I might as well put one back on.
Hope that this helps!
2009 M3 E93 Silverstone II over Bamboo: 6MT, Tech, Premium, Cold, Premium Sound, Ipod, 19'' Wheels, OEM Exhaust Mod.