Valvetronic actually. It has the x moved forward like the bimmerworld and ess x-pipes. Better exhaust scavenging which gives a little more torque, and seems to change the sound to be a bit higher pitched. They also claim they use HJS cats on the catted version. Cost is really good compared to other x pipes, especially the catted version.
I don't have any real data on people running this midpipe, so its kind of a gamble. The formula sounds right. I haven't installed it yet, so I cant say if it delivers in real life.
Only drawback so far is they claimed they were going to put the cats in the secondary position, but put them in the primary position.
https://valvetronic.com/products/e9x-m3-midpipe
I'm trying to replicate the below setup. To me this is the best s65 exhaust note I've ever heard.
It's using a ESS x pipe plus a corsa rear. I already have a corsa rear, and I suspect pairing it with the valvetronic x pipe should yield a similar result. Already sounds great with test pipes.