I have the Zard. Your saying 'not the noisest ... just something pleasant and deep', sounds to me like a very good overall description of the Zard. So, here's my review.
LOOKS: There's an element of subjectivity here, but I think the Zards are easily one of the best looking systems out there. Those 50mm fat pipes are just gorgeous. I have the titanium cans and their build quality is flawless. One sticking point is maybe the end cap design. It's different and some people think it's too different, but I quite like it and like the way it gives the exhaust an original look. Another issue is that the cans are quite long so if you have a tail chop they will stick out beyond the tail but this happens with almost any system.
SOUNDS: I had heard that the Zard had a deep note which is one of the reasons I bought it and in this I am not disappointed. It is deep, and don't kid yourself, it's loud. I rode with a guy on the weekend who had Termi slip-ons (no cat), the first time I'd seen the Termi on an S2R. I was really surprised. The Zard was louder and I liked the character of my Zard's tone better too. For me the Zard has three distinct sounds. There's the 'idle rumble'. This is very sweet. Because it's so deep it's not so offensive to the neighbors who'll have to listen to it starting up. All the same I am careful about starting it up too early in the morning simply because it's a loud pipe. Then there's the 'power on' sound. This is kind of a roar, quite typical to what you'd get with any good system on a Duc. You only get this sound when you're accelerating. Once you're cruising at any speed you'll barely hear the pipes because the wind sound it louder. And lastly there's the 'power off' sound. This is a note that comes in when you throttle down or use engine braking. It's a real booming sound and I love it - my favorite Zard sound.
BUILD QUALITY: Ah oh! Some issues here. Let me say that my build quality was perfect but I know another guy who's Zards came out of the box with a small dent in a can and a scrape on an end cap. So, before you hand over the cash, make a careful inspection of every part and you'll be okay. Another issue is end cap color. The titanium Zards ship with the silver end caps. The CF Zards use to ship with silver end caps then with black end caps. For the CF guys it turned out to be a bit of pot luck whether you got the silver or black end caps, so if you have an opinion either way you may want to make it clear to your dealer exactly what you want.
THE HEEL THING: Yep, unless you take measures there's a good chance you will melt your boot. I ride with a boot that has a soft rubber sole and many times I was leaving rubber on the pipe. I didn't want to hide the pipes up with any type of guard so my solution was to glue a two inch piece of black leather to the inside edge of the sole of my boot. I never had melting problems again. The leather may scorch a bit but it doesn't leave any mark on the pipe.
OTHER NICE THINGS: The 'Zard' sticker peels right off if you don't like it, not like some other brands cough<Arrow>cough. Also, the pipes will get hot, but the titanium cans never get more than pleasantly warm so passenger riding is no problem.
TILT: I need to qualify all I've said above by saying that I'm not keeping my Zards and will be changing to the Arrows soon. There's three reasons for this. I've gone back to liking the twin stack look. To me it looks a bit racier. Secondly, the Arrow pipes are a bit shorter and I think work better with the cut tail. Thirdly, I want a pipe that sounds a bit more crazy. I have a really good regard for the Zard's sounds but I want something even louder, and I really like the popping sound of the Arrows.
That's it. A full and honest review I think ;D