I love my compound system!!
I started with Smarty Jr and was very happy. I could have left it alone, but didn't... so I ordered the ATS Aurora Plus 4000 Compound system, which uses the stock turbo, plus their 4000 turbo. Quick boost buildup, and 44-46 lbs of boost, cool EGTs, no smoke.
Actually, I didn't get the higher boost until I switched to Smarty Sr. Jr didn't give enough fuel to "light" the bigger turbo and I noticed no power increase until the switch.
I went with the 4000 series because had I gone with their 5000, I would have had well over 50 psi and at that point, it was recommended I had ARP studs, bigger injectors, and possibly a second CP3. Since that would have cost quite a bit more for an extra 50-100 horsepower, I didn't see the value.
Even now, I don't feel the urge to get that extra 50-100 hp. I just don't need it. When I tow, I can pull anything I have on my lowest Smarty settings and never break 1100 degrees. Now, during winter, I have Smarty on #1 and everything else set as soft as I can. During summer, I set it on #7 and use a light foot, or tire wear becomes an issue! I never timed how quick I get to full boost (46), but I would guess one second max.
I haven't had any mechanical issues with this setup, other than a frozen waste gate hose last year. This caused over boosting because my waste gate wasn't opening. It went away and never returned.
No leaks, problems, or anything else. I can't compare them to other peoples' compound setups, because I've never driven them, but mine works flawlessly. Other systems can/will give you more power, but with that extra top end power typically comes increased lag to spool up. I have no such problem, with more than enough power.
I haven't had my truck on a dyno, however I do have an app on my iPhone called "dynolicious" which uses it's built-in accelerometers and your vehicle weight to calculate HP, and it tells me I have 460 at the rear wheels on #7. I ran a quarter mile at 13. 6@104 without even trying hard. I may be able to go 13. 3 at the same speed with a better launch, but there was no point.
I would recommend their system.