yes. i just changed one. but it' a little hard to remove the hdd.

Yes it is possible to use the ODD drive bay with an SSD drive, but why do it such a way when you can have SSD as your primary drive (OS & Apps only) then store your data on a HDD instead ?

SSD is more faster than HDD thus having SSD as your primary (OS) drive will significantly improve the speed & performance of your notebook.

I'm not sure whether Low Yat have such caddy available but you can search for it.

My suggestions is to replace the existing HDD with SSD instead, a fresh install might be required. Then buy an ODD caddy drive bay to install your existing HDD and make it as your data storage.

Though you will be sacrificing the ODD & might be troublesome should in the event you need to access/read from a disc which your notebook doesn't have the drive for it.

it is possible to have ssd and hdd all together. just need ssd bay to fit in optical disk bay.. check garage sales. they did sell the ssd bay

no. g55's sata port for odd is not sata3. it's actually slower than sata2. (still good for hdd with replacement hdd caddy) only the hdd bay and msata slot are sata3.

not sure for newer models, but asus uses slower sata for odd usually. technically, there are huge differences in terms of performance. can you feel it? it depends on your usage.