Both lights look fine to me.
The Niterider has many intensity levels, but the Marwi has 12 V bulb (a guess based on running time, power and battery capacity), which would be a good thing in my books (nothing wrong with 6V though if you can easily find bulbs for it).

Given these two choices I would take the light with better battery condition. Buying used batteries is in general not a good idea. But if you have some way of testing the battery condition on each light (or can easily get refund) you should be fine.