I have never heard of such a website. I think such offers on websites lasts only for a short period of time specially if it is a website which provies a .com .net or other top level domain names for free. If you are looking for co.cc domains which are free then just type co.cc in your address bar.
Its hard to know unless yo utry, yes some of sites have hidden aganda like forced adverts and popups, but if you search you will find some good one no doubt.
I have visited the site in your post and I think it might be a good choice for testing purpose. It goes with a not bad PR of 3 though it have not be updated for a long periods. Have a nice day,
After seeing your post, i have tried it... waiting for reply from them. i wil be posting here after getting their reply. I hope it won't be scam , if they given me a website
from what i've heard, i wouldnt recomend the site - the terms and conditions are less than desireable, they can cancel your site at any time. a good alternative is FreeDomainsForBloggers.com, they only put one ad on your site (after the first 2 months) and they don't cancel your domain if you dont meet the terms and conditions - they just don't renew it at the end of the year. a far better option.