I have been using Sente for over a year, starting with version 5 and now version 6. I was an endnote user for a long time switching to Zotero for a short while. However, I discovered Papers and Sente. At that time I found Sente superior and bought it. Superb interface, easy to use and you can cite directly in a number of word processors. Sente is also one of the best tool to archive and retrieve pdf articles (I have over 2000 of them). It has many more options (automatic search, …)
I have not been using “blundles” for my library but rather folder and files. This is to make sure that Sente and DTPO play nice together; I index (and automatically update via a script) my Sente folder in DTPO.