I have a Seloc manual for my older Merc. I've used it quite a bit, it's similar to a Haynes. However, I'm told by those with more experience that it's best used as toilet tissue, and the only manual worth the paper it's printed on is the original Merc manual. I'm a mechanically inclined amatuer, the Seloc has helped me at times and left me scratching my head at others. Would the Factory manual be any better? I have no idea!
So to answer your question, I don't know!
I am inclined to buy the factory manual at this point though, to see if I can sort out some electrical issues. With two books I'm likely to end up twice as confused!!