I don't use mine as frequently as when I first got it, but it's well worth it, especially considering how affordable they've become. I've done it to control the doneness of delicate cuts (flaky fish & backstraps mostly), as well as a long duration soak for a larger beef roast. I think the big sirloin beef roast I did was the best because I ran that thing at 128° for dang near 24 hours, and it turned out spectacular. I've also used it for easy food prep to travel. I've rolled smoke on some ribs before for a couple hours, then pulled them off to sous vide cook them. Freeze for a trip, stuff into a cooler, and end up where we're going. Pulled them out of the bag, heated on the grill, and they were a quick meal after a long day of driving.
If I had it to do all over again, I would buy one that was much shorter. The one I have has a fairly long probe, and it was difficult getting a vessel that would accommodate it. Ended up buying a cheap aluminum stock pot that's pretty well dedicated to sous vide. There are sets out there now that are a combo unit of the immersion circulator + a tub.
Another consideration is your plastic bag option. Ziploc works in a pinch, especially for some short duration stuff. But you really need to use a vacuum sealer for a long soak. If you go the Ziploc route, definitely use the freezer bags. They're much more durable and you don't risk a leak. That being said, the couple times I used a Ziploc, the water bath did end up smelling like the food I was cooking. I couldn't tell that there was a leak of any type, and my food wasn't soggy and waterlogged, but there was some sort of breach. I've never had a breach with anything I've vacuum sealed. The water is always clean when it's done.