post-BC Frost Mage view:

I think it is worth noting at this point that since BC came out and there are Jewelcrafters out there, the dagger looks a lot more appealing. You're no longer looking at a level 60 cap anymore where you might end up using that neck for quite a while, and the dagger will help you grind more efficiently.

As for the neck, look in the AH or ask a Jewelcrafter to make you one of these if you can:

https://vanillawowdb.com/?item=21790 https://vanillawowdb.com/?item=21790

At least as a fire mage, I am already wearing the Ruby Pendant of Fire, and have been since level 48: https://vanillawowdb.com/?item=21764 https://vanillawowdb.com/?item=21764

The necklace is an upgrade, but not a huge one. I'm frankly disappointed in the trinket. Having another button to bind and a thing to click on which just doesn't help that much, I'd rather skip. Compare with the Diamond Flask for the equivalent warrior quest which gives a large boost for around the length of a typical difficult battle: https://vanillawowdb.com/?item=20130 https://vanillawowdb.com/?item=20130

In short, the fire trinket could use some buffing.

I think that the trinket is the best thing there. The necklace and dagger are easily replaced fairly soon, whereas the trinket can last you well into outlands, since trinkets are so much harder to come by.

Post TBC these items are all pretty useless:

Necklace. If you look at https://vanillawowdb.com/?item=20966 https://vanillawowdb.com/?item=20966 you can see you get 7 more spell damage by using a charge, as these things cost about 1g to make (or 50s to buy on AH from a levelling JC) then this a nominal cost of just 5-10s a charge. This item also buffs your group so it better for instances.

Trinket. In comparason to https://vanillawowdb.com/?item=21769 https://vanillawowdb.com/?item=21769 this thing is just an embarrasment. It's once only use is pretty poor and will not contribute any meaningful damage over time. The mana back is nice but with mana gems, potions and evocation I rarely run short of mana, even in long fights. On use trinkets like this one I find rarely get used as often as you might think, I would prefer a simple passive trinket like https://vanillawowdb.com/?item=10659 https://vanillawowdb.com/?item=10659 to this.

I doubt I would bother replacing my https://vanillawowdb.com/?item=7714 https://vanillawowdb.com/?item=7714 with this. Chain casting Improved Frostbolt (2.5 seconds casting time) will only produce an average equivalent of 6 MP/5 which is pretty low. Given that you will not be casting FB's in a row and will be mixing in other spells then you really won't be getting much mana back at all. Another way of looking at this is that you will be getting an average of 3 mana back per cast of FB - that will lower your level 50 FB from 225 mana to 223! Look at it compared to this dagger https://vanillawowdb.com/?item=20647 https://vanillawowdb.com/?item=20647 - which you can get at level 54 by popping into Silithus and asking any random 60+ to help you kill and elite for a one-step quest on an inn poster.

Basically these items need a serious buffing, I wouldn't use any of them. Compared to some of the better items for other classes in the level 50 ST class quests (eg. Diamond Flask) I find the Mage ones a big disappointment.

I would be inclined to say that of the three the Fire Ruby is hands down the best of the rewards.

I think we can agree the mana return on the Glacial Spike is not worthwhile considering other options.

The Necklace is easily replaceable as you can see above.

The Ruby however, improves your mana efficiency, returning as someone said an average of 250 mana every 3 minutes. This is roughly 7 mp/5, though it will end up being slighly more useful than that as it will come in larger chunks, which could mean an extra cast.

The 100 fire spell bonus may seem only useful for Fire mages, but I know that leveling my Frost Mage, there is one fire spell I cast very frequently. Fire Blast! Frost is short on instants, and Cone of Cold is short range and rather mana intensive for a single target. I tend to finish off mobs with Fire Blast even as a full frost mage, as well as make use of the instant cast to do big Frostbolt/ Fire Blast Shatter combos. To make use of this trinket a simple Fire Blast macro can be used to minimize the hassle.

/use Fire Ruby
/cast Fire Blast

As instants get 42.86% spell damage, you'd recieve about an extra 43 damage on Fire Blast whenever the trinket is up, as well as the mana back. An extra 65 damage on a crit in a Frostbolt/Fire Blast shatter combo.

Hardly useless for a leveling Frost Mage!

I would encourage any leveling Frost Mage to take the Fire Ruby for juicy Shatter combos

As a class-specific quest, this does not count toward Loremaster of Kalimdor.

Someone quoted that instant casts get 42.86% spell damage. Does this apply to a brain freeze instant fireball?
My guess would be it does because ultimately it is instant.

Is this quest given after you get the dust stuff form the Belfs in Azshara?

As of Patch 4.01, all class quests for the Sunken Temple have been removed