One thing to note is that backup engine monitoring requires multiple probes for many sensors. Anything resistive (oil temp, fuel, etc) can't be shared between two monitors, no matter what brands they are, since the engine monitor powers the sensor.
If you're looking at Dynon for backup, you'll probably only want a D100 from us. Even in the clouds, most people can get down safely without an engine monitor, but a second ADAHRS can be a lifesaver. The D100 is $2400 and includes the full ADAHRS at that price, unlike the $1995 that keeps getting quoted for the MGL equipment. It seems clear from the original post that Ben was looking for backup attitude.
Of course, another option is to get the D180 from Dynon and use it primarily as an engine monitor, and the MGL as your PFD without any engine monitoring. You could then switch the D180 to split mode if anything was to happen to the MGL.
You have a lot of options, and no, you are not crazy for wanting a full, second attitude instrument in your plane when you fly IFR. Dynon recommends a backup from a reliable source any time IFR is expected.
Since you also indicate that you really want to fly IFR with your equipment, you should also talk to each manufacturer you are considering and see if they are OK with you using their equipment for known IFR flight. Many manufacturers specifically state that their instruments should not be used for IFR.