I looked at getting one a couple years ago, as I don't have many places left on my car to save weight.... unless its a track only car rarely ever driven I would have definitely gotten the higher end one with built in battery management to prevent the over draining and over charging from the alternator. One over drain by accident and it would be lost. And of course over charging is bad, as everyone knows. I think it was around $700-$800 for one of those batteries from Lithium Pros, only weighed 5.5lbs or so. Throw in a charger and you're looking at around $1,000. I then found a Deka ETX 30L Big Crank motorcycle battery that has 400CCA for $100 and weighs 22lbs. Braille sells basically the same one for 3x the price. And compared to an Odyssey PC680 that has only 170CCA the Deka has a lot more juice.
So my question became saving 16.5lbs for the Deka compared to the Lithium. At $900 difference that comes out to 54.5$ /lb. Which really isn't that bad when you are out of things to do to shed weight. However, I had a heavy 50lb battery and saved 28lbs going to the Deka for $100. At 3.6$ /lb it was a great bang for the buck.