For general use, they are in theory thief-proof because you can take them everywhere with you. The downside is they're expensive so you HAVE to take them everywhere with you. Leave them out and they'll get stolen. For that reason I think the happiest I've been is with a dirt cheap bike in Japan. Didn't even lock it properly (just a key built into the frame) and could park it outside any old shop or restaurant for hours. Super convenient.
For general use, they are in theory thief-proof because you can take them everywhere with you. The downside is they're expensive so you HAVE to take them everywhere with you. Leave them out and they'll get stolen. For that reason I think the happiest I've been is with a dirt cheap bike in Japan. Didn't even lock it properly (just a key built into the frame) and could park it outside any old shop or restaurant for hours. Super convenient.