Like the Smart Alpine, the Mega Jul does an excellent job of assisted locking when the climber weights the rope or while rappelling. You still need to keep your brake hand on the rope but it's a godsend when your climber decides to hang-dog the route since there is no braking effort once the device locks.
Feeding slack to a leader is comparable to an ATC and less fussy than the Smart (and one of the reasons I now prefer it over my Smart Alpine.) I'm not certain, but it feels like the Mega Jul locks up more quickly than the Smart - something to consider if your leader needs a soft catch.
Rappelling will require some getting used to as the device will lock on the rope and you control your descent by lifting on the thumb loop and letting slack go with your brake hand. Unlike an ATC, I don't back up the Mega Jul with a prussic of autoblock.
If you are changing from an ATC, expect to spend some time mastering smooth lowering and rappelling. If you take the time, the device becomes as natural as an ATC.
The best feature is if anything happens to your belayer while using the Mega Jul (think of rock hitting their noggin or being distracted by nearby hotness -I know that would never happen) and they let go of the brake end - you are not going to free fall. For me using an ATC feels like driving a car without seatbelts.
This product is much smaller than it appears in the photos. Paying out rope is smooth, rapelling is smooth, lowing is smooth, auto lock feature works great. Guide mode is not as easy to take up rope as the ATC Guide or Reverso but works fine. Stainless steel construction means it won't shed aluminum powder on your rope. Not as smooth when rappelling on a single line but still does the job.
This is a very innovative, light and effective belay device. Its nice to have an "auto locking" device that is so small, unobrusive and effective. I've used it on ropes from 8m to 9.9m. Its been smooth and hassle free.
I really like the concept of the Mega Jul. It does a great job at locking the rope and feeds rope very well. Unfortunately, the wire pulled out after only 2 days of cragging. I was lowering my climber by pulling the device up with the thumb loop when the wire popped out of the device body. Luckily the device locked up and my climber was never at risk. I had to use an extra biner to finish lowering in 'lever mode'. If Edelrid is going to give the wire a function they need to do a better job at making sure it won't pull out. Hopefully I can get a refund.
The device is easy to belay with, in lead and guide mode. Rapping in autolock mode is jerky, and can be quite difficult if you're on a steep face with the full weight of ropes hanging down. Rapping in regular mode works well.
Biggest problem is that the thumb loop release breaks off. I've had two Jul devices break now; a Megajul and a Miocrojul. Thumb loop broke off of both of them, making them very difficult to release.
I have a grigri and a cinch but I like the versatility of one device to belay and rappel. The Mega Jul does both and is pretty intuitive. I have had quite a bit of trouble unlocking the device when the climber falls on an overhang and/or can't unweight the rope. It is pretty jerky when it does unload. It takes some getting use to in order to smoothly lead belay, but that is pretty typical for auto locking devices. The Stainless steel construction is nice for durability and weight.