A small percentage of the population, maybe 5-10%, don't see as well with the goggles because the length of their eyeball is different from the average person. Eyeglasses prescription has no effect on whether the goggles will work for you. Even those 5-10% of people with the 'wrong length' eyeball, still see very well, but might have difficulty reading their depth gauge or something like that. Some people with astigmatism can see better with fluid goggles than they can see on land with glasses, because corneal defects have no effect underwater.
So, what other disadvantages are there?
1. If the water is very cold, you tend to get cold faster because you lose heat through your entire face & eyes
2. Personally I like to take off my mask once in a while and expose my face to the air. Taking the goggles on and off (repeatedly) is not practical unless you are filling them with sea water.
3. Walking over precarious rocks to get down to the water is difficult and more dangerous when wearing the goggles because they slightly magnify on land, and because you lose a bit of peripheral vision -- peripheral vision is used by your brain to balance your body when walking.
If you fill the goggles with tap water, the chlorine will burn your eyes. If you fill the goggles with distilled or purified water, your eyes will still burn because the water is not the correct pH (incorrect salinity).
Filling them with seawater (if you don't wear contact lenses), can be either very comfortable, or not, depending on which ocean you dive in. Here near Vancouver, the water is not salty at all--similar to your own tears. In the med or in Florida, the water is very salty and will burn your eyes.
Eric Fattah
BC, Canada