Sonokinetic make great libraries, and I've had nothing but good experiences with their service and support. I have Grosso, Vivace, DaCapo, Toll and Ostinato. They are great, and all see heavy use...except Ostinato.
It's probably it's just me, but I find Ostinato to be a bit artificial and lifeless, and quite rhythmically limited. There is nothing it can do that I can't do just as easily (and more realistically) by loading up a spiccato/staccato patch and recording ostinatos the old fashioned way. I dunno, maybe I need to take another look at it...