Originally Posted by Mike@N54Tuning.com
The difference is BMS doesn't use a "flex fuel" sensor. Which means you don't need to cut or work with fuel lines (introducing possible fuel leaks) to install it. From their perspective a flex fuel sensor is an unnecessary complication when you can use auto learning strategies (monitoring advance and fuel trims) to get the same basic information. The drawback with the BMS approach comes during extreme changes in ethanol content. Like if you accidentally put in 91 octane instead of 100% E85 AND forget to reset the auto learning (which takes 3 seconds in dash) you may pickup some engine knock the first time you stomp on it until the learning algorithm realizes the fuel has changed.
On the tuning end if using more than 40-50% E85 they suggest their flash along with the JB4. You load the BMS flash at home in your driveway. You do not need to remove and ship around your DME. When going in for warranty work you can also unload it from your driveway. When new maps and tricks are made you again can load them in your driveway without shipping things around and having down time with the car. Simple. Plus, the device they use for the BMS flash maps, the Cobb AP, has a killer resale value if you ever sell the car.
This is what sold me on the flash!