A lot of people have reported having adverse effects with this app as it consumes more than it saves. Haven't tried it personally though just echoing what i've heard.
Possible.
It depends on what schedule they put it on.
When I used JD (free version), you couldn't control too many of the battery saving options, like put it on a longer schedule, or set the night schedule, etc. So it's possible that those who don't see a battery savings were on the limited JD version which doesn't control their phone as tightly as paid version (Ulitmate Juice) allows them to do. YMMV.
Anyway, JD gives a big number of how much battery time I have left (e.g., 17h23m), which I take with a grain of salt. I do like JD because I can set it to control when my non-essential apps get internet connection, and most importantly, with UJ, I make sure that apps that I think have no business connecting to the internet are BLOCKED from data connections. I'm pretty sure JD saves battery because all apps are on the same schedule to connect, instead of connecting willy nilly and prevents unauthorized access to data.
I use JD in conjunction with Juice Plotter so that I can see how my battery usage is trending. Helps me identify probs immediately. For example, I found after I installed Missed Message Flasher, my phone was draining rapidly at night as I slept, which was not what it did the nights before. Everything went back to normal after I uninstalled MMF.
I'd recommend using JD and see for yourself if it does drain more than it saves.