Yes, it is more expensive than other drybags, like most things BMW. With that extra cost comes extra convenience, and nothing but exceptional quality and design - also like most things BMW.
It's 100% waterproof, (the main compartment, even though there's been reports that the outside pockets are also waterproof, the zippers don't look like waterproof one's, therefore I pack things that can get wet in the outside pockets, ie; cooking, and fishing stuff. It has a built it strapping system, and comes with 3 sets of 4 straps, small 6", medium 9", and long 14". ( I use the small one's)
This allows you to use the size you need without having extra webbing flying around. It can be strapped down with 4 straps, or if you have a BMW with a tail rack it has 2 straps built in on the bottom that you slide your rack through, allowing you to just use 2 straps on the front to mount it securly - easy on easy off. The wider strap is for our bikes, the smaller one is for a K1200R, I know because a buddy of mine used it last weekend on his K-Bike for a 2-up trip. I have mounted it with 2 straps method and it is very secure, thought the pics are of Plan B without the tail rack. I opted to move it as far forward to help with my CG, and give my back a little support.
The hybrid hard/soft design is great helping the bag keep it's form, while still being very lightweight and expandable. Having a flat bottom is nice, you could even troop a laptop in there if needed.
It includes a shoulder strap, and has handles built in that zip into their own little pocket.
I ended up buying it with a credit I had at a dealer, I might not have ever spend the cash if it was out of pocket, but if it won't break the bank for you I highly recommend it, it's a sweet bag that's very convenient since you can get in it without removing any straps.
With some help from a few compression bags I am able to pack everything I need for a (summertime) camping/fishing trip in this bag, including a kermit chair - minus the tent that goes in a H2W bag strapped to my forks.
You can buy one from Chicago BMW @ 20% off for $169. Buy a couple of other drybags, with rokstraps and you're not far off from the price this one....
a North Face 2 man tent because I lost the poles to my Mountain Hardware Lightwedge 3 tent on my last trip. The tent and poles goes on the forks in a Helen2Wheels tent bag, secured with 2 Rok Straps. 
