This is only good from LV55 to LV60. After this point Pole Grip triumphs this every time from LV60 to LV75, no matter what. The double attack increase is not to be underestimated. :D
"I imagine this would be the best grip for Steel cyclone because of the STR/VIT modifiers."
It's not, considering how after you WS, you have inferior DoT because of a lack of Pole Grip. There are several posts covering why Mythril Grip +1 is inferior to anything but multi-hit WSs on Allakhazam. Not to mention, most single hit WSs get a very substantial accuracy boost, negating the Accuracy+2 which is clutch in making mythril superior for WS.
its not totally useless i mean, say your a ranger and its your first 75 job and you dont want to buy an axe grip for your fire staff, this is your next best bet. while not he best its a cheaper decent alternative. for melee 2handers i will just stick to my pole grip though.
A good note on this and Steel Cyclone with Warrior - If saving up to 300 TP or planning on a Warrior's Charge for whatever reason (SATA tank, ..fun, etc), this IS the best grip during those circumstances, providing maximum damage output. Still a great grip, but yes, very situational as far as that is concerned.