This is really simple guys.
First the facts:
1. Since Silicone is not intended for human consumption there is no need for the manufacturers to place labels on the product warning of potential toxin leaching. The only reason some will state it and some wont is for an advertisements.
2. Most silicones (brand by brand) are manufactured through the same process and are capable of cross contaminating.
3. Anything other than 100% silicone will deteriorate under salt water and will FAIL.
4. Any silicone not created specifically for aquarium use can and will most likely carry additives to avoid deterioration due to sun light, mildew, bacteria, or salt water, PH, or micro-sized animals. These additives will harm your tank over time.
Second... The question:
1. How much money will you save buying cheap silicone at a home improvement center over buying the right stuff from a LFS?
2. How much money will you spend putting all your corals in your tank?
3. Is the savings worth it?
There are some things I go cheap on. But if it comes to risking the health of my corals/investment.... I won't go cheap.
In the end it is your choice. BTW I worked with a chemical engineer for DOW/Corning. These guys, among other things, make silicone.