1%QA on multihit is +0.06 to fTP
2%TA on multihit is +0.06 to fTP
Assuming it marginally decreases value of DA its around 0.11 to fTP so a little higher than elemental belt which means if you dont need accuracy this is the best WS belt for every WS that used elemental belt.
For Thief, Af3 Head/body/legs, Ballerines, Brego hands and tiercel neck is 25% haste without a belt.
I think I would actually TP in this if I had the above gear. Seems far from useless as I doubt THF is the only job that can exceed the cap by 6-7% with the advent of zelus and the like, just have to factor in oppurtunity cost on other stats.