The cabin curtain gives you some extra protection during the rain and keeps it from getting too windy in the main cabin. This is the first time I have had it on the Jeep and got a lot of rain. I had shoved some towels behind the seats to cover areas that were exposed to the elements and it worked without much of a hitch. Water did gather on the top of the cargo cover, but it rolled off when I drove the Jeep. The towel was damp when I pulled it out when I got home from work.
One thing I like about the pair is that the cargo curtain slides onto the cover via a ridge, so you get a nice seal between where the curtain meets the cover. The only downside to using the curtain, other than losing some of the open air feeling, is that it takes some time to get it on with the Trektop NX "Bikini". There is a bar that goes across the back of the cover that needs to be removed to get the buckle of the strap through. It is very tight. I was able to pull the buckle through when I removed the curtain, but even that took a bit of work. I may use the cargo cover without the curtain if I am pretty sure we won't have rain.
Jeep Wrangler thoughts
Jeep ("Just Empty Every Pocket") Wranglers can be taxing for the wallet if you want to customize them. I was lucky to find someone to donate a few pieces that I could use and it saved me several hundred dollars, so it was hard not to take that "saved" money and spend it on one of my "wishlist" items (and I have several), but I am trying to spread out the cost over a few years before I pay it off. The problem is my wishlist is growing faster than I checking stuff off. :) I never had that issue with any of my BMWs, they were great off the lot and I really didn't feel like they needed to be changed. Of course, the stock Jeep is great, too. It just begs to be modified, though. That is really where some of the fun comes in, but having a stock soft top Jeep with the top down is what I remember from my first Jeep, so it ain't all bad!