there is also the cloak of the brotherhood (http://classicdb.ch/?item=5193) and the bandit shoulders (http://classicdb.ch/?item=10405) to make a really complete set.

This set all drops in the instance The Deadmines in Westfall. This is a set worn by many level 19 twinks.

For Horde twinks, it can be tough to get to the instance. I recommend traveling to STV and swimming upward. Just watch out for Alliance as you near the instance.

well, the set is BoE except for the chest. Embrace of the viper is largely BoP.

The interesting thing about this is that it makes it viable for twinking, if you put an armor kit on the leggings, you can still take advantage of the set bonus value... which I THINK supplies better AP for melee, and only slightly less stam then the embrace set. It's pretty good, all in all.

I need to look at the numbers again, though.

Edit:
ok, comparison of typical twinking items vs. defias leather.

http://classicdb.ch/?item=10399 standard.
Unless you're alliance, this is the standard item for rogues. SOME will go for the tunic of westfall for the agi (http://classicdb.ch/?item=2041) , but this doesn't really hurt you.
http://classicdb.ch/?item=10403 vs. http://classicdb.ch/?item=6468
18 AP vs. 5 agi and 6 stam. I think the new version of the defias belt may be BETTER, but you lose dodge.
http://classicdb.ch/?item=10402  vs. http://classicdb.ch/?item=19969 or http://classicdb.ch/?item=1121
The boots hurt you probably the worst. You either lose out on 8 AP and 5 agi worth of dodge, or you miss out on 10 stam and a BC enchant.
http://classicdb.ch/?item=10401 vs. http://classicdb.ch/?item=10413 or http://classicdb.ch/?item=6586 or even http://classicdb.ch/?item=7284
The gloves also lose you between 1 and 8 AP, including between 4-6 agi worth of dodge. They contain 1 stam, as opposed to the 4 in a scouting glove of the monkey. The red whelp gloves actually give a proc that's equivalent to 1-1.3 dps per minute with 1.5-1.9 speed daggers, the equivalent to about 14-20 AP. Being a 5% chance to proc, though, and the fact that a ton of rogues use shadowfang/cruel barb at this level, (and with shadowfang's relatively slow speed for a 1h), no one really uses the red whelp gloves.
and lastly http://classicdb.ch/?item=10400 vs. http://classicdb.ch/?item=5961 you lose 2 AP and 5 agi worth of dodge.

The set bonuses, however, make up for this by the expertise and AP bonuses.

The arcane resistance offers a slight buff to resisting polymorph, which is nice, but not dependable enough to be consequential unless stacked with more. The armor makes up for a little bit of lost agi, but again, it's not that great a bonus.

From typical twink gear, you're going to be down about 100-200 hp or 4-8 AP, (depending on what you pick) you'll also lose around 10% dodge from the agi. In return, YOUR attacks will gain about 0.95% chance to not miss, not be dodged, not be blocked, and not be parried. for warriors, pallies, shammies, and pets, that's 3.8% more on the table. for hunters and rogues that's 1.9% more. (correct me if my figures are wrong)

druids you'll likely be hitting from behind anyway. =P

Regardless, it doesn't look like a bad option, by any means. and it's more stylish.

For those of you who are comparing the Embrace of the Viper set with the Defias Leather set, at the time of this writing...

Defias Leather Set (complete)

314 Armor
+10 Strength
+9 Agility
+14 Stamina
+28 Attack Power
+5 Arcane Resist
+2 Expertise

Embrace of the Viper (complete)

333 Armor
+18 Strength
+26 Agility
+24 Stamina
+7 Nature Spell Power
+4 Expertise
+6 Spell Power
+10 Intellect

Those are the base stats without the combined effects. Since the combined effects will vary depending on your class (and talents in some cases) I leave it to you to do the math and decide which is best for your character.