Regarding the smart vs passive keys:
- If you have at least one key of either type that's paired with your Rocket, you can buy and pair additional keys. You should do that, so you have a backup. I keep my smart key in one pocket and a passive key in another pocket. That way if a key breaks, fails, or is lost, I can still get home.
- The smart key can enable the ignition and allow you to start the bike using the same method as any passive key. It doesn't matter if the battery is missing, dead, or the fob is disabled. It'll still work as a passive key.
- The downside to using the passive method to turn on the ignition is that it times out and turns off automatically. This mainly matters when trying to do things without the engine running, like loading a tune.
- If you're far from home with no key then, yes, you probably need a tow. Not being able to start without a key is by design.
- If you lose your only remaining key, you will then need to buy a new ECU as well ($$$). Don't cheap out--get backup passive keys so if you lose one you can get and pair a new one.
As far as what was wrong with mechanical keys, that's a matter of opinion. But issues included ice in the lock mechanism (that stranded me a couple times), failed lock mechanisms (stranded a couple of friends), accidentally leaving the key in the ignition making theft even easier, breaking the key off in the ignition (met one guy who did that), etc.