More exhaust noise and less power.

The cross-over helps the exhaust pulse be shared by 2 mufflers. With 1/2 the sound going out 2 exits the work is cut. The BMW mufflers are particularly good at silencing, meaning they are particularly "stuffy". If you send the entire exhaust pulse through a single exit, then the engine will need to work harder to "breathe". Not a power drop like 15% (maybe not even obvious to the rider), but enough to notice fully loaded and crossing a mountain range.

If exhaust leaks on the non-clamping style are getting to you, then wipe the inside ex pipe spigot with regular silver silicone gasket sealer. (Not the red "high temp" stuff !!) After waiting 30 minutes you can easily remove the excess on the exterior of the pipe. Once the engine is run, the silver silicone matures to a chrome color that is very nearly invisible. This will stop even minor leaks, last you well OVER a year, and not become an "eye-soar". And it's VERY inexpensive, and allows quick assembly/ disassembly.

Hope this helps.