I'm fairly new to all of this, so I'm admittedly not completely knowledgeable about the options that exist for buying good links. I heard about links-management and here's my experience. I used them for about three months and paid about $200 or so. You can adjust a few parameters that affect how much you pay. I was starting with a site that was a couple of years old, with good content but no external links. I hit the first page of Google for my main keyword after about three months and, as you might expect, it made a huge difference for me. But some of the links are spammy, and it's possible that on the next Panda or other update, my site might fall in the rankings. Nevertheless, it's been three months and I am still between #1 and #3 for the keyword that brings in 99 percent of my site visitors. In total, I have 4-5 words ranking 1-3. and about a dozen in the 4-10 range. My position in the Google results has all come from the links.
If I knew of something better, I would try it because I have had some billing issues, but they fixed those. It's only email support but they've answered all my messages so far. I would say the service works, but the question is how long it will work for. You do have the ability to input a paragraph of text before and after your link where it's placed. I've checked a subset of the links I paid for and they are all there.
I hope this helps someone. My summary is OK but go with someone else if there's someone better. It works, but the question is for how long. My sense is they are expensive, but I don't have anything to compare it to.