That would be me. We don't do complete turn-key conversion packs yet; you'd need a couple other components if you used our hardware. We have done a couple comparisons between carbed and EFI cars, and in many cases the power output was the same but the drivability, area under the curve, and such were much better. Here are some things to consider in an EFI package.
1. Completeness. Some people want to buy a package that has everything ready to just take out of the box, bolt on, and go. Other people would rather select each component and match it to their needs. Obviously, the second approach is more work; the price can come out different either way, but sometimes an off the shelf kit may have some parts sized wrong to fit a particular goal.
2. Origin of the system. Some packages are built around refurbished stock electronics off something or other - Mass-Flo, for example, uses Ford 5.0 Mustang electronics, and there's several companies that use GM hardware. (I'm not aware of any built around Mopar computers, although I believe the Pro-Jection's throttle body is related to a stock 318 TBI.) Others use aftermarket computers (the FAST or MegaSquirt systems in the above links are only distantly related to anything used by OEMs). General rule, a factory computer would be cheaper, while aftermarket computers were designed to be tuned by someone who doesn't have a million dollar budget and an engineering degree.
3. Tuning type. This can range from no tuning (not quite as bad as a carb you can't rejet if you're using a mass air flow sensor, but can still reduce your options) to the screwdriver adjustments on the Pro-Jection (an approach no other surviving system still uses) to tuning with a laptop. The last is kind of like a carburetor with a different jet for each combination of RPM and vacuum signal - only you can change the jets while the engine is running at full throttle. Many of the systems out there allow you to use a wideband oxygen sensor to give the computer the ability to tune the fuel on its own once the engine is up and running, but I would recommend having a manual back up in case this goes wrong.
4. Feature set. A carb to EFI conversion really only needs to control fuel. However, you could add ignition control, which lets you dial in advance curves which completely disregard the limits of a mechanical advance mechanism and let you get the curve nailed down even better. However, while it's possible to tune the ignition without a dyno, you'd want to plan on some dyno sessions if you want to get it better than a non-computer controlled ignition. Other features you could get include fancy ignitions with multiple coils, making the computer control your cooling fans, built in nitrous control, sequential injection (timing the injector pulses, mostly helps with a smoother idle and better emissions, and a small gain in fuel economy), and a lot of other stuff. You have to decide if it's worth it, though.
