I think most demands go to general license.
If I'm right this was also covered in the blog some time ago, where statistics showed more favor for generic models.
It most likely depends on use cases, for example in a game a brand would be avoided in most cases and in short films or video/photo montages also.
But if it involves commercials for that specific item, then obviously they would not mind and need an exact copy.
So that's why maybe doing both is best because you could deliver something for all.
I don't understand you would need twice the time to make a generic copy, because you rely need not change all that lot to have a new model. Just make the copy and afterward change some design features that are hallmarks of the brand, and avoid using the brand name.
If you really need to go for one or the other I would bet on generic (always safe).