Why buy links or guest posts on high metric web 2.0 blogs when you can buy the entire blog itself?
Each one of these blogs is going to be registered to a unique email address using unique IP addresses.
What To DO With Tumblr's?
Once you receive the tumblrs, create a 300 word article regarding your niche site/ranking site and link to the site with the anchor text you want. This will give more power and authority to the DOMAIN, and help it rank better in Google.
Important: It is recommend to use VPN when accessing the tumblrs accounts to minimize chance of getting them banned.