I bought the Yellow (Underwear) , Blue (Clothes) and Purple (Lingerie) a while ago.
I remember looking on the website and really going back and forward for weeks. (It is kind of an investment, am I right?!) Then I saw them "in real life" in a little travelshop near me and bought them instantly!
Let me say I have not regretted it for one single second.
Before I had those mesh-type kind of luggage deviders. The Spacepack is a little bit more heavier, but are soooooo much better thanks to the "laundry side" of the pack (and the handle).
You do not lose any space due to your laundry. Just throw the used clothes in there and since they'll be in the same bag as you packed them, it's lots easier to have an overview of all your stuff.
When I return back home, I know precisely what I used and... what I didn't use! Every trip I take, my packing gets better and lighter. (Learning curve!)
Recently, my boyfriend and I took a 10-day long vacation. Normally I would have thought to need 2 big suitcases to check-in (with probably an extra carry-on)... Now, he used 1 blue and 1 yellow pack. I used 1 blue, 1 yellow and 1 purple pack. As simple as that! We could of have fitted in 2 cary-ons, but we used one check-in suitcase and one carry-on (to have some place for souvenirs).
Size wise, I'm in looove with the yellow pack. If you only can get one pack, believe me: you got to go YELLOW ! In my experience, it's the most handy size. It's perfect for a weekend or overnight stay. All of my clothes fit and I keep a lot of space in your carry-on for my beautycase, my shoes,... ! (Since it's for 2 to 3 days, I really don't mind that my underwear is mixed with my clothes.)
And if you leave for an extended trip, you could easily get away by using 2 yellow packs :)