If you spend on a good high frequency sine wave AC inverter they can be very efficient >90%
For me the the downside of a generator is having to deal with gasoline as much as the noise. But I definitely agree with you on the small Honda generators... They are amazingly quiet.
@Art Deco ...also keep in mind with the DC - DC converter is that you lose the safety feature of your charger in that it shuts down at full charge. There are ways to manage that like my DIY solar charger hack... But it's definitely more hands on with every charge