Metallic mercury is actually nowhere as hazardous as people want you to believe it is.

Now exposure to mercury vapor (such as actively heating metallic mercury) over a long period of time (months or a year to two) will have slow developing effects and it builds in your blood stream. This can have much more long term damaging effects.

Exposure to mercury dissolved into a solution. Particularly any solution that is permeable to human skin if exposed can prove fatal in a matter of weeks.

It's worth noting that mercury even in it's metallic form is always off-putting mercury vapor (even when not heated) however the level is so low you'd have to surround yourself with pools of it for weeks or months before inhalating enough to cause concern.

But metallic mercury isn't going to hurt you if you have it on your hands. It can't penetrate your skin. Just don't get it in any cuts. Cody'sLabs has done quite a bit of experimenting with mercury. I was going to link a video where he effectively washed his mouth out with a mouthful of dental grade metallic mercury and explained a lot of the scare society has put on it but looks like he took it down and I'm sure that was YouTube's doing.

Mercury when it enters the body goes into the blood but it stays in the blood. Being a heavy metal it's hard to expel but being in the blood it will be expelled over time so low exposure over many months usually doesn't result in mercury poisoning.

Something to be more afraid of is lead. Lead when it enters the body and gets into the blood stream and binds to your bones. Once it's in your bones it is very hard to get back out and as such the toxicity levels will go up much faster with exposure because of how much harder it is for your body to get rid of it.

Even then lead isn't all that scary either. Just don't go around eating paint chips or make a habit of sucking on a ball of metallic lead.

@Windows7ge I know, doesn't stop legalities and whatnot though. 

Yeah, you're screwed inside the US. I don't even know if you can legally sell any electronics here if they don't comply with RoHS (I'm not counting imports. I mean local retailers).

I couldn't find any of this from US sellers.  I had to get it from aliexpress, although they were pretty cheap.

I mean once it's installed in a product. If you made this "game pad" for disabled people and tried to market it as a product that's what I mean about RoHS compliance. I don't know if the US would even let you sell it being a U.S. based retailer/seller.

There would at least need to be a warning about mercury.