I have a Silhouette Cameo (not the latest model, but the software is the same). I bought it for about the same reasons you are looking into an additional cutting machine. I was choosing between it and a Scan N Cut and the price was one deciding factor. No-you do not need to join the design club to get designs--I usually buy them as needed on sale for 50cents each--you get them to save in definitely, plus they also have weekly free designs. You can join their club, but know that the tons of designs they offer include ones for 3D paper, scrapbooks, Heat Transfer, vinyl, fabric, etching glass, setting rhinestones, etc.
You can also design your own using a program much like computer drafting, and also you can (using a special mat) scan in designs from pictures, etc. You do all this on your lap top which the cutting machine plugs into.
You set cut depth, type, width, change out the cutting blade for different materials, and also can use a pen (either just a plain one or special ones) in the blade holder to draw out designs on the paper, etc.
you do have to stiffen the fabric for cutting either by fusing fabric onto stablizer (either theirs or basically just any fusible stablizer like Heat N Bond, etc) or (and I haven't tried this but have heard from others that have) something like Terrial Magic that you spray on to stiffen so it goes through the machine smoothly.
It does work fine on cutting fabric but I think the design needs to be somewhat less complicated to efficiently cut. I've also used it often with cardstock, vinyl, heat transfer, the pens or a drawn design, Their website has videos to show it in action.