I've got two of the TW Titan long batteries.
I've had them for two days, and been using them all day today (they spent yesterday charging.)
Here's what I noticed today:
1. It was great not to go dead.
I am often out and about, and with two short batteries I often go dead. It sucks.
Today I had one in my charger, a charged battery on my desk, a short on the atomizer, and a long battery in my pocket all day.
2. They last longer, but it sure doesn't feel like double the life.
So when I am at my desk, and my 510 doesn't leave my mouth, the double life translates to an hour and 15 minutes vs. the 45 minute life of a short battery.
When I was out and about, puffing here and there I really noticed a huge difference. When a short battery would go dead before long, the longer style battery seemed to last all afternoon.
3. The short batteries appear to keep a more consistent performance.
With the two short batteries which came in my starter kit I notice how great it is to have a consistent drag from start to finish.
The longer batteries are not the same. They begin bright and powerfully, like the shorties, but somewhere around 3/4 power they begin to dull and feel more like a 901. Since it's actually good for our batteries to be "topped up" like our carts, when I've felt this tonight, I have swapped it out. This limits the comparative time I've been able to use the batteries, but it's still really nice.
My observations are preliminary, and may change over time, but these are my first impressions.