The downsides I see with the chain drive are that it will require lubrication, although there are some automatic oilers available. The lubricating oil will be messy. It will require replacement but only after about 18,000 miles and that will be easier than a belt change. The other downside is shown in the photo below, although highly unlikely with a well maintained modern chain. The photo is of an old racing Morgan 3 Wheeler. There could be problems fitting a chain drive with an NVH kit as the BB isn't solidly mounted.

There are several plus sides as well, which is why I am seriously thinking about doing it, probably with a chain guard of some sort fitted.

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