I used the newmodeus caddy - I'd say weight is about the same.
Battery life is now measured two ways:
One, with the HDD unmounted. That way, I get better battery life than before thanks to running only off the SSD.
Two, with the HDD mounted and running - battery life is 30 minutes less - give or take it's not all that easy to tell. But I feel like I am getting a lot less.
Guesses for medium use at full screen brightness: Before mod, 4:30. SSD only 5:00, HD+SSD 4:00. Very approximate values, depends on a lot of things. When watching my usage, I can easily go 6:00 or 6:30 with the SSD only.