I found that I had to relax my face and keep it relaxed, adjust the straps once the mask was on my head (by pulling the two blue straps on either side outward), this gave the best seal (tight) and limited water coming in the bottom. A small amount still came in, but was easily exhaled through the valve around the mouth area. With practice this gets easier and more fun to use. I found the less I moved my mouth the better the results were (as it seals around the jaw area - you don't want to move it too much) - it takes practice.
I also strapped my apeman action camera onto the snorkel pipe and took this mask for a spin 4m down and was able to get some good footage and test the mask out. It fogged a little bit, but when inhaling again it cleared itself. Decompressing underwater (like with a traditional snorkel) was hard as you can't hold your nose through the mask and blow. However with practice this can be done using the small muscles behind the ears with the mask on. The water limit valve worked well and did not allow water down the snorkel pipe when underwater.
The straps were comfy and tightened up easily with a pull in one direction outward (once wearing). There was a bonus extra set of replacement straps, seals and valves in the package, earplugs, action camera attachment, action camera bolt and nut and a carry bag. Great little extras and very handy to be able to plug my action camera straight on without hunting for extra bits to connect it.
There is definitely a learning curve, but if your willing to persevere, experiment and adjust your behaviour slightly, this is one great little face mask. I recommend this for people who are a little adventurous and willing to put in the effort to get the best results out of the mask.