I just tried Juice Defender this week, and I've seen an incredible difference with battery life. Juice Defender saves my battery a ton. Just as any usual day I barely touched my phone. Without it I usually get 50% when I get home. With Juice Defender by battery life was at 86%.

 

EDIT: I guess the question really is, do _you_ get better battery life with or without Juice Defender? Try experimenting!

 

I don't use JD on my phone, but i use it on my wife's phone. She syncs her email and let's it run in autopilot.
JD won't turn off the wake lock for wifi. That wake lock will drain the battery.
I use the phone a bunch during lunch and when I get home I will have over 50% battery life. Rouge apps can kill the battery too. And auto killers,also. If it's for you, look into the main page for the Triumph. Whyzor wrote a great guide about saving your battery life. It's like fuel economy, if you don't use it you won't loose it. You would need to weigh the benefits of both sides of each choice as you go down the line.

 

I noticed the same issue also: JD (paid version) prevents deep sleep even when it turns off BT, WiFi. I reported this to the dev, who, after 2weeks, just asked silly questions (clueless):

Rolo42 ? Feedback and support

Which means that you have to manually toggle BT, WiFi anyway, effectively making all battery savers the same (toggle 3g only).

They do give you a week to ask for a refund; mine only took a few days after the request.

I also didn't like some of the other weirdness that came with it (needing some workaround to install software).