One of the most frequent questions users have when starting to research potential engine management solutions is "What do I go with?"
Reflash mediums are the most commonly used application, for all but the more complicated setups. Therefore, the dilemma ends up being whether an end-user should go with Cobb AP or OpenECU for their engine management needs. The purpose of this thread is not to debate which one is better, but to outline the differences, allowing the end-user to weigh the pros/cons of each and make an informed decision about which solution works best for them. In an effort to keep the thread more technical in nature, if you have a question about which one is better in your situation, please create a new thread (mention you've read this) instead of posting in here...
They are both reflash solutions, so the difference in tuning comes from the map contents itself, and the device in which the map is sent to the car; Cobb AP is a proprietary device used solely for ECU-related actions, where the Tactrix (OpenECU) uses a laptop which can be used for ECU-related activities, as well as everything else a computer can. There is a myth/belief that says OpenECU is for more computer-savvy people, but that is not really the case; if you can download/install software and read directions (the same thing needed for using the Cobb AP), it's pretty much equivalent in terms of difficulty.
Cobb AP retails for ~$600
A Tactrix cable retails for ~$175 (but requires the end-user to have/purchase a laptop capable of running ECUFlash/Romraider software)
Both can be purchased used for a discounted price. The Cobb AP marries itself to the ECU the map is loaded on, so it needs to be unmarried from the previous vehicle in order for it to be usable; Cobb can unmarry the device for you, but the cost of this (last I heard) was in the $200-300 range. If purchasing a used AP, you need to be sure the previous owner has properly unmarried the AP from their vehicle, or else you could end up spending more money than had you just bought one new.
Cobb offers free Staged maps for certain modifications with the purchase, where a Tactrix cable requires the end user to source their own map (free user-submitted maps on the Romraider boards, purchased, etc.). Cobb offers "real-time" flashing, which allows you to put a temporary map stored in memory to test changes without having to do a full write (it is erased and the ECU reverts back to the "base map" if reset); this makes testing map changes quicker. Tactrix only supports full writing. Both offer the ability to modify the map (with the exception of a locked map created by a professional tuner using AccessTUNER Pro). Romraider (OpenECU) has a strong forum community of fellow DIYers (and professionals) to help you with issues that you come about, as well as sharing tuning philosophies/methods. Cobb has a tech support line you can call with issues you come across. Modifying your map with either method can cause catastrophic motor failure. Either method can cause the ECU to be bricked if the flash fails. The Cobb AP marries itself to the ECU it loads a map onto; without properly unmarrying it, you will not be able to read/write to the ECU again without sending it to Cobb to unlock or finding another AP to borrow to unlock it.
You should datalog your car after flashing any map to make sure it is running properly. Both have the ability to datalog selected parameters from the ECU while driving. Romraider has a "Fast Polling" option which gives significantly more resolution than Cobb. While some will talk about the convenience of not needing a laptop to log when using the Cobb AP, when you factor WBO2 into the list of parameters, you will need a computer in order to poll that information.
Professional tuners can use either method (with proper licensing from Cobb), but some do not tune OpenECU due to the fact that their maps cannot be locked; their IP is left visible to anyone, and the end-user can monkey with the map. When choosing a reflash method, if you think a custom reflash may come into play at some point, you should reach out to the shop(s) in question and talk about what medium(s) they're comfortable using. For people that aren't in a close enough area for an in-person tune, e-mail tuning is an option with either choice.