So the trinket gives you 260 haste for 10 seconds every 120 seconds and passive 64 attack power.
Since 2.2 you need 15.76 rating for 1% haste so 260 haste give you 16.5% haste.
With 16.5% haste you'll be able to do a steady/auto rotation. But stacking this trinket with rapid fire will get your autoshot timer below global cooldown (1.5seconds) which would be bad for your damage.
So apart from the 64AP you get 16.5% haste for 1/12 of the time (if you use the trinket whenever it is ready).
16.5% haste should improve your damage by 16.5% as long as you can maintain your shot rotation. Most likely your damage will be a little lower as you will not be able to adjust to the new timing perfectly.
So the haste buff increases your overall DPS by 16.5% / 12 = 1.37%
Including timing issues and lag you should still see a DPS increase slightly above 1% when you constantly use the trinket.
So the question you have to answer is whether you other trinket alternatives boost your DPS by a higher amount or not.
Bloodlust brooch for example has 72AP (+8) passively. The use-effect gives you 278AP for 20 seconds on the same cooldown (2minutes).
So you get 278 for 1/6 of the time. 278/6 = 46.3 AP
The nice thing with bloodlust brooch is that you can stack this trinket with rapid fire to get even more out of the extra AP.
So to decide between those two trinkets you have to way 72+46.3 AP against 64AP and 1.37% total DPS.
This boils down to 54.3AP vs 1.37% DPS.
The numbers above are not 100% realistic since they assume perfect conditions (like using the trinkets everytime its available and adjusting perfectly to hasted shot rotations).
Now it gets even worse. Since I don't know how much DPS you do and I do not know how much DPS you get out of 1 AP I cannot answer your question, but I can make a guess *g*.
Lets assume a Kara-equipped hunter can do a total DPS of 700 (without pet).
I further assume that 1 point of attack power gives 0.3 additional DPS (including crits and pet).
With those numbers you get:
abacus of violent odds (1.37% dps increase) = 1.37 * 700 / 100 = 9.6 DPS
bloodlust brooch (54.3AP) = 54.3 * 0.3 = 16.3 DPS
As you can see bloodlust brooch gives a much bigger increase in DPS.
Even if the hunter can dish out 1000DPS the abacus would still do less damage.
So a lot of text but I'd say that the abacus is not a very good trinket for us hunters. It is hard to use (since you have to adjust the timing of your shot rotation) and it does not add very much DPS.
However I still love my
Dragonspine Trophy. This thing will stay for a long time in my trinket slot