Trying out the public beta right now. This is everything that Multifl0w should have been. So far I'm loving it, and the memory management seems far superior to Multifl0w's. Animations are fairly smooth, switching is efficient. Swipe up to close is another great feature.
The default settings are a little strange, however: double-tap to switch to an open app is silly, and it does not come with a default setting to open ProSwitcher with a button. Understandably but somewhat annoyingly the app shows blank screenshots for native apps which have not yet been opened after a respring. The effect of this is mollified by another great feature: the apps' icons and names are given right under the screenshot, which can help to tell apps with lists like Address Book and Mail apart.
And, best of all, it works with Kirikae! Right now I have hold home button set for Kirikae and hold sleep button set for ProSwitcher. But I'm not sure that this won't be reversed soon as I come to rely more and more on ProSwitcher.
The poor author of Multifl0w! Nobody's going to buy his $5 alpha-quality software when ProSwitcher in its first beta is almost flawless...and free!