They are definitely convenient. I was planning to use mine for steeping but decided against it since (for me) time and shaking seems to be doing the trick. UC's are great for stuff like cleaning
tanks (or dentures) but you can get something pretty much as clean without one, it's just going to require more work.
If you want to use it for steeping more quickly some folks have reported decent results. I merely don't because I've also heard mixed things about it, and I'm pretty satisfied with my mixing regimen. You'll have to decide whether it is worth it for you. I feel like my purchase was worth it for me-- but really as Letitia says, it's more convenient, etc.
Anna