M Unit: easy to install, rugged, and feature-rich. Yes, to the idiot lights. It is my opinion, that it is easier to create a new wiring loom from scratch when you use it unless, you fashion a mounting plate to install it in current electrics location. Even then, you can drastically simplify your wiring with the M Unit.
The only "gotcha" using it with our SOHCs is the horn button. Our horns are triggered by a GROUND interrupt from the handlebar switch. The M Unit wants to trip it with switched power. So, you can either change your horn type, or reconfigure your horn button, or, abandon the horn being controlled by the M Unit. (I re-wired my Horn switch). No big deal.
I also suggest a solid state Reg/Rec as an upgrade. Again, makes the wiring simplified with the M Unit.
If you don't want to create a new loom, it's still quite do-able, just have to cut and extend some wires. Whichever, it's all easy. Check out Blackfin5's 550 thread; he also used it and just finished installing his M Lock unit (keyless ignition switch). Uses RFID technology and helps clean up the electrics even further.
Feel free to ping me with any further questions, or for any help I can be. I've got 2 more bikes in my stable that are getting them installed too. The more the merrier!