In most cases, yes! A lot of people who use #21 have reported that six months after using it, the shine is still there and the water still beads up nicely. A few have even reported being able to go an entire winter, with salt covered roads, and in the spring they've still got a nice layer of protection on their paint!
Why would you say #21 is over rated? I've never heard of anyone that is disappointed with #21! It's easy to remove, leaves no dust behind, shines up nicely, hides minor imperfections well and is very durable. What more could you ask for in a sealant?