I am working to identify the problems with the lite version. There were a few code fixes (template issues) that were made and a few people had problems with this hack when installed in 3.6.x. but I have not been able to reproduce the errors. I do not think there are any security issues.
As for comparing the two products, SR Classifieds is a lite version that allows Ad Types of BUY and SELL in one level of categories. With SR Classifieds there is no way to charge to list an item.
vBClassified is a much more diverse product and has a completely different operating database. It uses a concept of Ad Nature and an Admin can add as many Ad Types as they would like that use the basic nature codes. The current Nature codes include NO PRICE, FIXED PRICE, and INCREASING BIDS. vBClassified also allows multiple images with lightbox, private offers system, public comments, bid retraction logging, Commit to Buyer options, Deal Pending and Deal Done systems, and more. It also features an incremental bid system like ebay and sellers or site staff can delete bids. You can compare the two on my site at
http://www.vbclassified.com and as you can see you can have both run on the same website as they do not use ANY of the same phrases, templates, or database tables/fields. vBClassified uses a system of credits that can be purchased with $Money or vBBux points and these credits can be set to various costs per category (including FREE). Credits are also optionally used to feature ads.
I am just starting to try to address the issues with SR CLASSIFIEDS lite. One issue I have noticed is that the whitespace is not preserved and I had to fix that in another of my projects but I need more time to trace the code to find the error.
If you join my site at vbclassified you can try the LITE version and see what it does and you can try the premium version as well. Both work quite well, it just depends on your needs.