I like my Opti but I 'm enamored with the Freedom due to its light weight, small size, that it's rechargeable, and ability to treat water in a Gatorade bottle which my Opti won't fit in.
The Ultra is heavier but I appreciate that it is similar to the classic design so I can just cork a Smart Water/Aquafina bottle, flip it upside down, and treat. Being able to treat twice as much water on a single charge isn't bad either but most of my trips are under five days and I can recharge the freedom if need be.
Price, I believe, is the same. I'll buy from REI due to the return policy if they crap out on me.
Any recent users care to weigh in on the good, the bad, and the ugly with these two? I plan on purchasing soon after the holidays.
Edit to add: I will be able to recharge either one in the field with an 18650 battery and Miller ML-102 Universal USB Smart Charger. At least I will in theory as my Panasonic batteries are supposed to arrive today.
http://www.fasttech.com/product/1137904-miller-ml-102-universal-usb-smart-charger-version