Cooking pot with lid for saving gas but that doesn't overflow?
The device which "releases the pressure automatically" is a normal pot. You don't put the lid fully on, you leave a small gap on the side. It is sufficient for practically all cooking. 

And yes, if it is still overflowing, you should reduce your temperature. Not only don't you win anything by cooking it at such a high flame that it boils over even with a gap, you are also wasting gas - which you said you care about. 

As for the device you linked, it is a very different thing. It cooks food faster because at higher pressures, it can be heated to over 100 Celsius. Cooking with it is very different from cooking with a normal pot, and it is up to you if you want to get into it - but not having to leave the air gap is not a typical reason for it. 



Trying to clear this thing up after some discussion with Jefromi: 

You are pumping more energy into the system than it can hold. You have a few possible solutions: 


Stop pumping that much energy into it (reduce the heat). It is wasted anyway. 
Have an open system - one which can't withstand pressure and bleeds it off as soon as it starts rising. This is the "pot with a gap in the lid" method, no matter if you are using a standard lid or one with the gap and catch lip built in like suggested in the other answer. 
Have a closed system which can keep in the energy (it will produce pressure higher than atmospheric pressure) and release it after you are done cooking. This is what a real pressure cooker is for. It does come with some advantages, I've also seen claims that it is more energy efficient (I don't know if it is, really), but it is really a completely different mode of cooking. 


What you are proposing is a mixture of 2 and 3. Now, if you make it very close to 2, such that minute amounts of pressure are built up before venting, you are still expelling that same energy from the system, and haven't saved it in any way. You just have created a more complex (and so more expensive less failsafe) device, there is no reason to not stay with solution 2. If you make it very close to 3, in that you hold in a lot of pressure before releasing, you automatically make it almost the same as pressure cooking, only with some useless venting of energy, so there is no reason to not build a real pressure cooker. Basically, anything in between 2 and 3 is going to be worse than both 2 and 3. 

The most practical solution, used by countless cooks over the world, is a combination of 1 and 2.