Never heard of them
Their website has some information under Contact
In a non critical situation I'd probably give them a test drive.
Surely there are some customer, travel magazine, reviews out on the internet someplace.
Added: got curious so I looked at the Yelp entry. Avg of around 200 reviews is about 2 stars. But the reviews are from 1 to 5, all over the place. So this is very dependent on the local car rental company that is working under the Nu brand. i didn't look for specific Orlando area reviews.