Hi,
I have one in California, actually a "kit" as I talked to Sparta years ago about shipping me one. They not only wouldn't sell me a Spartamet and don't sell bicycles in the US because of unfair product liability laws.
So, I have this Spartamet like bike here in California and I went to talk to the DMV, our motor vehicle regulators, about what I have to do about registration and what license I need. Turns out you need a motorcycle license and the bike can be registered as a moped but you still need liability insurance. I went to take my motorcycle license test and there is a riding ability section. I hopped on the bike and was going to ride it around the course and the examiner laughed and said don't bother, no one will stop you with that thing. Turns out, he was right.
I mostly use it as a bicycle with the engine off, I have it set up as a 15 speed with alpine gears. The engine really helps in climbing some of the hills in my area. I heard at one time that Sachs made a Saxonette engine with two speeds. That would be perfect for steep hills.
The best thing, I really enjoy riding, I sold my car because I never use it anymore. As for longevity, I chatted with an Australian who has used these to tour most of Australia and the Western US. He has over 35,000 miles on one of his. They are very reliable, they have to be here, nearest parts are 6,000 miles away.
My only concern was that the two stroke engine was polluting a lot. Also smelled like two stroke oil, just wasn't good around other cyclists. So, I retrofitted mine with a catalytic converter, so no smog, but still had the smell of two stroke oil. I got a fragrance that drag racers would use in their nitro methane mix. Now the engine exhaust smells like fresh lemons.
Oh, almost forgot, I got stopped by a guy a couple weeks ago who wanted to know what type of electric motor I was using. He is an electrical engineer and builds electric bikes and because it was so quiet, had no idea it was a a two stroke engine.