Some users have recently had their accounts hijacked. It seems that the now defunct EVGA forums might have compromised your password there and seems many are using the same PW here. We would suggest you UPDATE YOUR PASSWORD and TURN ON 2FA for your account here to further secure it. None of the compromised accounts had 2FA turned on.
Once you have enabled 2FA, your account will be updated soon to show a badge, letting other members know that you use 2FA to protect your account. This should be beneficial for everyone that uses FSFT.
If you just got the EXOS then I see no reason not to use the included solution. You already have it and it works. If you are refilling the system then I say it's up to you.
I obviously used the included solution when I got my EXOS. When the system needs to be flushed and refilled I'll probably just use distilled water and water wetter or something similar. Then again, I'll probably mess around with modding the EXOS later on also. I really like the setup being external in the casing and will probably try to keep it that way.