I want to get a tuner for my Dodge Magnum. Should I? Are they worth it? Do they really work?
I have seen them on shows like Gearz.
Well are you trying for track or street legal? If you mess with the computer on a street car and get caught expect a BIG fine and impound of your car.
Stacey David is a lot of fun, but I don’t think that it will work well on a Dodge Magnum. I am absolutely gobsmacked at the thought of owning an SL-C, however. Even if it only has an LT-1 engine. Yow Yow! The drooling starts here:
Hand held tuners like those from SCT or Diablosport are good for extracting the most benefit from other aftermarket modifications, on a stock or near stock, normally aspirated car, alone they don’t do a whole lot. Once you get into forced induction or even more extensive engine modifications then they are worth getting. When I had my Mustang supercharged a tune was necessary as even running the engine on the stock ECU tune with the supercharger was recipe for disaster (it would be way too lean). So I had the car dyno tuned, which resulted in two custom ECU tunes. I have a conservative tune that I use every day, and a more aggressive “race” tune that leans out the mixture more than the conservative, daily driver tune. The “race” tune is worth an extra 20-30 HP though. Both these tunes were given to me on a CD-ROM (the daily driver tune was uploaded to the car’s) ECU, I put them on my computer, hooked up my Diablosport Predator tuner to the computer and upload the ECU tunes to the Predator. Using the tuner I can upload either tune to the car’s ECU. I can also adjust other parameters like the idle speed, rev limiter, traction control, speedometer calibration, rear end gear ratio setting, spark timing, etc. It also functions as a data logger, and OBD II scanner. So it’s useful to have around. But like I mentioned before, on an otherwise stock vehicle, don’t expect much from just uploaded one of the “canned” tunes right out of the box.
I would forget about it. If you improve the performance…the fuel economy drops like a stone. If you manage to get better fuel economy then the performance is gone.
I have a Diablo Predator tuner for my 2006 300C. IMHO, the tuners are worth it, especially if you’re tech-minded. You can adjust a lot of parameters, including ones that can potentially damage your vehicle severely, so some research is advised before doing any major tinkering. There are preset/pretested tunes that you can apply to your car. I have a mild tune that I leave on mine, for 91 octane gas, and I have the option set to firm up the transmission’s shifts. The difference is noticeable in the car’s performance and driveability. Of course I have to use premium gas or risk spark knock harming my engine. My fuel economy actually went up slightly with the 91 octane tune, based on previous results using just 91 octane gas and the factory tune. Your economy will of course suffer with more extreme mods and if the additional performance encourages you to put your right foot down more 
The tuner I have also acts as a scan tool and allows data logging, and monitors a ton of the car’s parameters. I can see what temp my catalytic converter is running, for example, and play back data from the engine’s sensors, including knock sensors on a hard acceleration run to determine if potential damage is occurring.
I have an older tuner, but I can still download tunes for my car and apply them through the tuner’s serial port. I can restore the factory tune to my car at any time, which is a good idea if you’re taking the car in for service, especially if you have a factory warranty left.
If used haphazardly, you can destroy your car with one of these. If used with a little common sense and not going beyond your knowledge or comfort level, you can extract a little more performance and enjoyment from your vehicle if it’s stock, or adjust to take advantage of aftermarket mods, as FoDaddy said. My car is stock, mainly because I already have enough horsepower to get me in trouble and better things to do with my cash these days.