I have been using them for about 5 months. Pay right away. Took a couple of months to fill the space, but when they filled it they kept it filled. They seem to do a good job getting their customers to renew. I was going to delete after a month or so because I thought it would take forever to fill the space. Fortunately I didn't.
Yes, they are quite good from a buyers perspective. They offer organic links and fair prices. From a sellers perspective they take a 50% cut and offer a so-so referral program. So if you are a buyer go with text-link-ads and if you are a seller go with AdBrite.