Is the mSata really worth it?

I don't know if you found that out already, but you don't have to worry, as that's not the case. What Defer-Write does is prevent just that - it prevents the synchronous write to your RAM cache and the SSD simultaneously (because you can't just write to cache, you need to actually write the data to your drive, eventually). What Defer-Write does is cache your data writes in your RAM (basically you write the data to your RAM). It then defers that written data (hence the name) to your drive, and only moves it to your drive later on. It also consolidates that data to one single write instead of multiple little writes like in everyday usage. See here:
FancyCache Demo - Reduces Writes to Solid-State Drives

This not only doesn't decrease the SSD's life cycle, it actually improves it, allowing to keep working for longer. The only (quite major, really) downside coming out of Write Cache + Defer-Write is that if a crash occurs (like a bluescreen, especially true if you do a lot of OC tests), that cached data is lost and therefore - corrupted. This can be relatively harmless, like some game information or a large file being copied, but it can also be catastrophic, like an important system write, which will corrupt your whole OS and prevent you from booting up and force you to reinstall.

I hope they can prevent that from happening on later versions by excluding important system writes from caching.

 

I see, but keeping it read-only while benching is still better, because after the benching is finished it'll write all that data wrote to cache in the RAM onto the SSD and then delete it.

Samsung's SSD magician benches the SSD after every single optimization, gotta watch out on this if you have a Samsung SSD and uses their utility weekly and want to enable write cache.

 

Aside from the benching, which I couldn't care less about, how is it for everyday use? Will you notice any difference?

 

Ummm, not exactly

You enabled only read-cache, so nothing is written back to your drive. What read-cache does is copy the data you are currently 'reading' (loading a game, for example) to your RAM, and the next time you'll run that game (if you don't reboot) or if the game requires that cached data while you play, the read-cache will serve it from your RAM instead of your SSD, providing a much better performance. If new data is loaded along the way and you're running out of cache space, it will remove the least used data (LFU in the configuration) or just the first data that was ever written (LRU - essentially making a FIFO: First In, First Out) to get more caching space, but again - nothing will be written back to your SSD, this whole party happens and stays in your RAM. In that scenario, writing to the SSD is simply a standard writing.

huluwafu, as you know, the RAM is so much faster than anything else, it's like comparing a sedan to a fighter-jet. That being said, the SSD can be compared to a Bugatti Veyron, so even though the jet is much faster, it still requires properly preparing for take-off and activating all the safeties first (the whole caching process), while the Bugatti can just go. Therefore, the everyday usage difference will be a few single digit seconds less, nothing you'll notice that much, but still faster. Caching vs standard HDD, though, that will be a whole different ballpark.