Sure the set bonus isn't very desireable, but I would still do the long grind for the Kris. The only dagger that is better than this for casters is the Claw Of Chromag. Unfortunetly, not all people can play this game to the point where Chrom is on farm status, so this is the alternative.

Long grind you say? Imagine how long it takes to go from all blues, find an MC guild, get geared enough for BWL, work through BWL and down Chromag enough for this to drop, then bid enough or roll high enough to get this. That takes much longer than grinding exalted from Twilights and doing a bit of AQ20.

So, in my opinion, the grind is well worth it.

Blizzard is actually changing the set bonus in Mists of Pandaria to 2% Increased Shadow and Fire Damage, instead of 5% Increased Pet Damage. Not sure why they decided to change this seven years after it came out.

The set bonus wasn't very desirable back then, and it seems it will be changed to a passive school damage bonus (which is quite puzzling).
The cloak hasn't a memorable feel to it and won't be looked for transmog as much as the dagger, whose model is only shared with the rogue quest one, and might catch an eye.