Is this product compatible with a Nikon D3100?

Http://www.jessops.com/online.store/products/67558/show.html

I've seen it listed on a forum as being compatible but the website doesn't seem to show the D3100 as an option.

Http://www.jessops.com/online.store/products/67558/show.html

Just call the store and ask them. They probably haven't updated this web page for a while since the Nikon DSLR models listed have long been discontinued.

Technically yes, it is an iTTL flash. You will find, however, that it is a rebranded piece of Chinese junk. Not worth any amount, let alone what they want for it. Save your money.