It's something you don't need. It gives you a longer CD HS to new dalaran than the one given for free. It gives you are ilvl ring equal to what you'll get at max level. Old Dalaran ring was at least unique in the sense that there wasn't an alternative to it like there is with the new HS.
The ring serves very few purposes. It makes you not have to upgrade a ring while leveling. It makes you have a pre-raid BiS for some classes and it gives you an extra HS to a place you already have one too. If those things aren't worth 250k to you, don't buy it.
Inflation is everywhere now due to garrisons and Blizzard needs to pull a lot of that money out of the game, hence these items and the 10m cap on BMAH now. I know of 8 people with 50m+ gold. That is enough gold to last forever for multiple people, or to get sold illegally RMT style for 10-12k USD. Both of those things Blizzard doesn't want, so they had to come up with a solution to clearing money out of the game. This is what they came up with.
Buy it or not, that's up to you, but Blizzard intention wasn't for everyone to get this ring.