I'm guessing these tk domain names are free. Personally, if I owned an article directory, I wouldn't allow such free domains to be linked too (that includes squidoo!!). Plus isn't tk pretty lame. Didn't they put up advertisements and stuff? I could see them hijacking all the traffic for themselves. Just buy a domain name.
Now, you can switch off their ads. Works like simple frame redirect. The address display your tk address, but you are on the merchant's website with your affiliate ID.
I agree, there are so many bad .tk sites. plus a .info domain can be had for like $2 for the year, just give up on coffee for a day and buy one.