I've been running an Atomic since the beginning of this summer and have had nothing but great results. They are by far the least obtrusive of all the aftermarket kits when installed because their ECU and fuel pressure sensor, unlike FAST's, are built into the throttle body. The only external "box" you have to mount is the power control unit, and that has the footprint of a large mobile phone. The harnesses were all of very nice quality and seemed to be loomed a lot tidier than the FAST and Holley offerings. One last feature I liked was that the TB has a built-in throttle return spring, which is a nice touch in-terms of removing clutter and making it into an integrated package.

Drawbacks or dislikes aren't numerous, but I do have them. First, you can NOT use the PWM feature with any fuel pump other than MSD's because they use a proprietary frequency. Two, if your motor has a very poor vacuum signal, count on using a single plane intake only. The system will tolerate down to 9" HG of vacuum, but MSD recommend single planes in low-vacuum situations. Third, the horsepower limit of the system is definitely there with only 4 80PPH injectors. The more expensive FAST EZ EFI 2.0 runs 8 60PPH injectors, so that's the only game in town if you're going over 640 horse N/A with a kit like this.

The driving characteristics of the kit have been superb. I'm running my Atomic on a 512 that pulls 12" of vacuum and I don't have any issues. The car started on the first try and has only ever stalled twice. Both of those stalls, however, were during the initial learning phase of the ECU and have never happened since. Throttle response is ultra-crisp, cold or hot it starts almost immediately, and I've gotten a decent gain in fuel economy. You can set your own A/F targets for idle, cruise, WOT and fuel enrichment on throttle tip-in (like an accelerator pump). I honestly haven't had a single problem with it in-use. It is expensive relative to what you get, but I suppose that's the price you pay for a succinct fuel injection package wearing a brand name. All I know is that I don't regret buying it, and I don't miss the carburetor at all.

Let me know if you have an further questions and I'll answer them as best as I can.