The Chainglider is not sealed, and therefore it will not keep out sand and soil in places where the wind blows that along – some of the world’s most popular bicycle-travel routes are like that. Complete disassembly was then required in order to adequately clean the chain. Plus, even under ideal conditions the Chainglider required more frequent adjusting than I wanted to do.
It doesn't keep out water either, but it still works quite well in the prevailing weather conditions in southern Brittany where I live and it does keep most of the wet muck off the chain.
Fine, dry dust isn't a problem where I ride, but I imagine this would be a good reason not to use a Chainglider in some places. The sand on the tracks in the dunes that I occasionally use is probably too coarse, because the Chainglider works quite well on that.
I've had one on a utility bike for 12 years now, and have progressively fitted Chaingliders to all the family bikes that are compatible (it won't work on the Brompton folders or the large visitor bike with vertical dropouts and a chain tensioner).
The main advantage for me is increasing the intervals between chain maintenance by a factor of about 3, maybe even more. It probably also increases chain, sprocket and chainring life, but this is difficult to prove because the transmission had already been used on most of the bikes to which I have fitted Chaingliders.
Another advantage is keeping chain oil off clothing or skin.
I eventually just took the Chainglider off as too much bother, and tossed it into a bin on the roadside, and I can’t say that the remaining 6,000 km of that tour were worse because of that.
I was very sceptical when I first tried one, but reckoned it was worth a try at the price. And had it not worked for me, easy to remove and discard, even when on tour.
Though having used Chaingliders for more than a decade, if I ever ride in fine dust, nowadays I would probably remove it and keep it to refit later after leaving the dusty area and cleaning the chain.
Nomad Mk3 and a belt drive
None of the 8 family bikes with Chaingliders are compatible, so that would mean new frames or expensive frame modifications, plus all the specific parts for belt drives.
So belts aren't an economic option for me. It might be different for someone buying a new bike, or who already has a belt-compatible frame.