I don't know of them and to be honest I don't concern myself all that much with futures trading. So Digitex is new to me. However, when it comes to futures trading I immediately have to wonder: actual Bitcoins or just futures-derivatives? Since they operate on a blockchain with a token I assume it's going to be actual Bitcoin but I think there are regulatory problems surrounding stuff like this. I think the Winklevoss twins have been trying something like it for a while but haven't gotten permission, so what makes Digitex special?
Another thing that concerns me is the zero fees. There's no such thing as a free lunch, and especially if they are blockchain based then who pays the miners or nodes to keep validating transactions? After all, miners/nodes need to be paid in crypto or they will mine something else. So there has to be money made in some way, shape or form. If it's not from the trading fees then it will be from another source. It is very likely that their 'automated market makers' are in fact bots who will, without being transparant to the users, skimp off of micro-trades from every trade you make. Basically whenever you want to buy something for $100, you'll end up getting it for $101 (or something) due to bot interference. I think the popular Robinhood app in the USA does the same thing in order to finance themselves. On the interface it will say 0%-fee but what they don't tell you is that everything is just a tiny bit more expensive.