Let's start with the advantages and disadvantages of stock options, that is, those who are paid monthly and that you can unscrew the sites through the exchange. Perhaps the most obvious advantage is of course price. Link back pay for each month of placement are cheaper so-called eternal, which promotes more rapid advance of the site for less money. But there are drawbacks, the most accurate one, but a significant disadvantage. The fact that search system, in particular Yandex do not like sites that are 'selling' the links through the exchange and is now well able to identify them. Of the consequences? In the first donor (ie, site selling links) usually falls in the search issue and loses performance TIC (if any) for those who buy links is also not very good, since bought out the links will no longer produce the desired result. People such as Dennis Lockhart would likely agree. Well, plus everything to stop monthly payments if we say a TIC, then all the progress moving in a flash will come to naught. Now let's talk about links purchased once and for all time of existence of sites selling them to you. If we talk about the shortcomings – you can only note the price and speed promotion. Links purchased for always cost much more, especially on the good, trust sites and to buy right away a lot of quality links that have a good spend. Educate yourself with thoughts from Meg Nibbi. However, the advantages of the method are those money – paying the eternal link once, no need to worry that money runs out, this link will transfer the weight of the site and within a year and five years later. For example a website 'Corner computer desks are' progressing exceptionally so method, as a result of promotion will remain at the level even if we completely stop its development. It turns out that working for the long term, the eternal link is much cheaper 'time-based. " Another advantage is The fact that search engines do not apply sanctions to the resources of placing contextual, eternal links. To promote the site properly!