Absolutely worth it! In my opinion of course.
The most difficult thing about the ASK is getting over the price. That was an extremely hard pill to swallow. I thought Microsoft was out of their minds charging $149 for their TypeCover but Apple topped them.
The ASK is the perfect option for anyone who wants the lightest, thinnest, on-the-go solution for the iPP. On my 12.9 iPP, I have both an ASK and a SmartCover (for those times when I know I won't be typing anything more extensive than a tweet).
I wanted my iPP to be as thin and light as possible so I opted for a clear skin (not a case or rear cover) on the back to protect against scratches and provide a better grip. I used clear Con-Tact paper. Works great. Looks great. stupid cheap.
Unlike other keyboard options for the IPP, the ASK is easy to detach, flip around, and reattach (so that the rubberized surface faces outward). This allows me to use the iPP in full "tablet mode" with no hassles.
Two main complaints that others have about the ASK are, lack of backlit keys and lack of a row of dedicated keys for various functions. I personally have not found the lack of backlighting to be a problem and as for function keys, there are plenty of standard key combinations that provide some of those features that are actually MORE convenient than having dedicated keys.
To determine what key combinations are available in an app, simply press and hold the Command key... a window will appear displaying what combos are available.