Simply put, SSP is about 10 times larger than the earlier release. And you can hear that the sound is MUCH more accurate and defined. Mind you that this is a small chamber strings group and not a symphonic string section, so it has to be used accordingly.
Also a crucial difference is that the original product only gives you one section of “generic” strings, which means no divisi, no violins, violas, cellos, basses, just a unified “string patch.” Might work for background “pop strings”, but it’s not very credible when the strings are exposed or they play more complex lines. Furthermore, SSP comes with a lot more articulations, round robin layers, expression layers etc. Finally, it comes with a lot more automated patterns (including the option to program your own), although I’ve never been a fan of those (IMHO they still sound mechanical), so to me the latter is a moot point. But then again, some people believe it’s actually SSP’s best feature. As usual, your mileage varies.
SSP is still NOT competitive with the best strings libraries on the market, but, to be fair, it’s not as expensive and it’s not meant to be used to recreate classical music on a computer.
P.S. How is your question on-topic? For someone who blasted me (and most likely reported me) for allegedly going off-topic, your post comes off as mighty hypocritical (neither SS or SSP are free VST’s.) But hey, I answered your question anyway, and wouldn’t even have made a fuss out of it, if you didn’t attack me before. Peace.