My first exposure to belt drive was a Kawasaki that I bought in 1987. Fantastic experience w/that motorcycle, and it was an easy leap for me to accept belts on bicycles.
Belt drive is wonderful in winter. I do nothing in winter except to let my bikes drip dry inside. No lubing, no rusting of the chain, no crud in the (internal) gears.
The OP asked about slippage, and no one's commented yet on that. The belt does need to be "in the zone" with respect to tension. Too loose and you get slippage under load, and too tight leads to friction and noise. Hoping I don't get crucified for admitting this in a public forum, but I just "wing it" when adjusting my belt tension. There are tension gauges, and a phone app works pretty well, but I have good experience going by feel.
Belt drive is wonderful for people who just want to ride and enjoy a few miles now and then without having to fuss a lot with cleanup and lubing of chains. My daughter is a perfect example. She's not a bike enthusiast. She just likes to ride to work and back -- year round, including in winter! --and for enjoyment on sunny days. A low maintenance bike that needs no oiling and cleaning is perfect for that application and is easy to store inside her apartment, because no worries over grease on the carpet.