Yes, permanently locked. Bounded to one device you choose.
If you purchase it as a downloadable version I think you can install it on as many PCs as you like and on one device. And it won't be illegal. But I think it also depends whether you are going to use it for personal usage or lets say you are going to install it on the companies PCs. If this is the case I think it would be illegal. Better to consult Garmin. Most probably for each computer should be purchased a separate copy.
If you want to install it on other devices you need to purchase additional subscriptions for the other devices. Same applies if you purchase it on a DVD. Only available online I think.
But it also might depend which City Navigator - Europe, USA, Russia, Australia... you purchased. Different versions might apply different rules. Those Garmins....
Regarding arounding the limitation I think the only way is to change the prebult device Identification Code or ID. Not so hard. But there is also a but. Each installation of CN provide specific files needed for the model/series which most of the time does not apply to the other series. So this way is not very suitable.
Other way might be just to install it on an SD card rather than to a device. By this way by swithing the SD card you can use it on as many devices as you want.
Also install it on a removable HDD....