Not sure about you guys, but on Bismarck these are ~3500 Gil, and I can NPC them after they're used for 2747 Gil.
That's 753 gil spent for 10 teleports; about 75 Gil per. Normally you'd be paying 1000-2000 Gil and you would stand around shouting for a Tele. These are great even if you do have the OP Warp, as you don't have to travel back to your home country to use it, and it's likely cheaper as well.
this is a great ring for anyone to use to level their NPC with. God knows we all have to spend a good amount of time in the desert(s) leveling. With just a signal pearl you can only call NPC once a day. Pair it with this ring, and it's a free ride to level your NPC and you're close to Rabao for a job change/warp when done. ^^
As Kiyodesu said they're great to make your teleports a lot cheaper, but if you're below level 65 you'll still need to shout or ask a friend. However if you're 65+ this is a great item to have lying around
Yes, when you break it down it's cheap per teleport but it is one-day use. If one tele is all you're looking for it's great, but you're going to have to buy more if you plan on doing something else.