Not really. All generations of the Sub basically sound the same. The Gen 3 has some updated internals and an updated Join button. The only reason you would need a Sub (Gen 3) is if you wanted to use two Subs with your Arc setup. At least one Sub (Gen 3) is required for a dual Sub setup.

So I’d like to read your knowledge in this case… my Sonos system are… arc / 2 era 300 / Sub mini but I’d like to change my sub mini for the Sub 1 gen. I get an amazing price in eBay but the question is… exist any problem with the 1 gen to paring with the last generation of speakers? ( about connectivity or kind issue) please I need your advice! Thanks 

The Sub Gen 1 will work just fine with the Arc.