I have one and think it's amazing!
My friend who has an all mountain board says the SL is a little stiffer after riding it and many way the SL leans more towards the freeride side, while the proto leans toward the freestyle side. I've done ZERO park, so I can't comment on the freestyle.
It definitely has a steeper learning curve than a soft park rocker board because turn initiation isn't as easy. I found I had to pick up a bit of speed to turn it properly, so it might not be the best board for a complete newb. However, you say you can go down blues confidently, so it definitely won't be a problem for you. It's my first year and after a dozen times on the SL, I can go down blues pretty well.
Also, I crashed and skidded into a patch of rocks and dirt that wasn't blocked off by my local resort. Besides a few scuffs on the base, the board didn't get damaged at all! That's a testament to it's durability. Hell, I got more banged up than my board!
Some commented on the "jack-of-all-trades, master-of-none" type board that the SL is. Well, that's what an all-mountain board is supposed to be, right? If you want a one-board, all-mountain solution, then it's pretty hard to pass up IMO.