A GFCI saved me when my heater broke. As soon as the glass broke, I heard the thing click and the power went off. A $20 outlet from the Home Depot is worth nothing when compared to your life.
GCIF- Ground Falt Circit Introupter (sp?, google it)
You could use it and it will work perfectly fine. The reason they say not for aquarium use is because it doesn't have a built in GFI which will prevent you from getting shocked if something electrical is in the water. If you other power strip has a GFI, just plug your new one into it and you will be protected.
I do hope the above that the above post is a poor joke. Otherwise it is about the dumbest thing I have read on the web. Darwinian selection at work.
To answer your original question, you can pull as much power from an outlet as you want. Just don't exceed the amperage of the circuit. You likely have 15 or 20 amp circuits.
If you want, you can calculate the amps on the circuit (not just the outlet). However, unless you have a GIANT aquarium or are on the same circuit as the refigerator, you'll probably be OK. Aquarium gadgets don't draw that much power, generally.
So don't be afraid to use the larger power strip (but please find a GFCI!).
Wackydan, your quoting and responding to stuff like 2 years old, not sure how any of that applies to NewLuv4Fish's current concern. The overloading of circuits and daisy chaining extension chords has nothing to do with why the power strip in question says not for aquarium use. As I already stated, I am pretty sure its just a liability thing since they do not have GFCI. If you want to be safe then put in GFCI in. There was a long thread a while ago about the coralife aquarium powerstrips that say not for aquarium use. I never did check to see if any of mine say this. I use many powerstrips, none of which are certified for aquarium use. I did however install a $5 GFCI outlet in the wall and the strips are plugged into it.