SSD caching has worked absolutely fantastic on every system I've set it up on.
Really where it shines is the ability to use cheap 64gb SSDs, which on their own wouldn't really be big enough to install onto directly. I can build computers for customers and for $60 extra they can get the SSD experience without any of the hassles.
Also keep in mind that when using a larger SSD, the remaining space beyond 64GB is still available for your usage. You could have a 256GB SSD for example, setup as caching, but still have almost 200gb to work with to install stuff directly onto the SSD. No need to choose when you can have both.
I like to use SSD caching for the OS because there are a lot of files that end up on the main drive that would simply be wasted space if they were directly on an SSD. Temp files, downloaded files, unused windows system files, pictures, documents, etc taking up gigabytes of space on an SSD is a waste. I don't like having that claustrophobic feeling of being space limited on my main hard drive. I should never have to think twice about installing something because of the space it might take up.