IMHO, the off brand batteries can be a hazzard. They are made in China and not necessarily manufactured to the Japanese safety standards. New batteries made in Japan to the latest safety standards go thru some really tough tests to make sure they are safe and won't overheat or burn and explode.
In the end, its just a matter of the risk you are willing to accept, if they were commonly catching fire, we would know, but it does happen.
I still use my 3-1/2 year old LP-E6 Canon batteries that came with my 5D MK II in 2008. They hold about 60-70% charge, so I only get about 600-700 exposures on a battery. I have bought third psarty batteries in the past, they lasted 6 month and died. I also bought a used camera that had two third party batteries with it. One was dead, the other had overheated in the camera and I had to drill it and take it out in pieces.
When you consider the risk and overall cost over a 4 or 5 year period, the Canon batteries will cost less than 6 or 8 sets of junk ones.