When we say clean power, to me that means voltage and frequency.
I took a different approach, and just power my critical loads from battery in the case of an outage. Think Tesla's PowerWall, or in my case, an SMA Sunny Island that powers a critical loads panel either from the grid or a battery (and I have 4 8D AGM batteries). You could always have a generator that separately powers loads that aren't as freq/v sensitive (eg: motors... furnace fan, fridge, freezer, etc). Many generators also are paired to batteries to provide surge loads... so that a 10kw generator can start a large A/C (where surge load for the compressor motor and furnace fans -- think 2x typical running loads) might be too high for a specific generator, but the running loads are not)
Or, a different implementation would be to use that inverter in series with your generator. Depending on the generator's specific type of "dirtiness", the Sunny Island can be configured to condition generator output,auto-start/stop the generator, and manage generator load (eg: don't overload):
White paper
A Sunny Island costs around $4000-5000 depending on how much wattage you want to protect (4.5kw to 6kw)
Related, What has the experience been with running a UPS when the generator is On-line? Has anyone found a good UPS that will go off battery and condition the generator output? (dual conversion)
I have spoken to quite a few UPS companies and am really surprised that this seems to be something that most haven't gotten inquiry about.
The most common answer is "the UPS can be configured to accept a "dirtier than usual" signal". My experience is they still won't go off battery when the generator kicks in.
Most common generator I have run into is 10-15KV Generac propane or natural gas.
The problem is the sensitive electronics (security system / home controller) will shut down once the UPS battery is dead - even when the generator is providing plenty of power.