Useful? Yes, probably if you are at a desk all the time - and that first one at the $40 price point is actually tempting me a bit, but I don't know. How well do these things actually work? Bluetooth is notoriously clunky. It seems like every time someone calls me from their car using bluetooth there are issues.
I prefer hard-wired headphones w/ a mic for calls longer than 10 minutes or so. I assume you've got an iPhone based on the products you linked below. The factory headphones that Apple provides are not bad, but if you are looking for an upgrade you should check out
this product by Shure. You would also need to couple it with their
sound-isolating earphones. It would get a bit pricey, but great sound quality and infinitely more portable and useable than a handset device. Plus you'd get a great set of earphones you can use for anything, not just phone calls.
And for what it's worth - I've got a "fancy office phone" in my office and it's really not much of a quality improvement over my mobile.