I had purchased the D301 model and a 3 in 1 diffuser (ceramic..back flow checker and bubble counter) back in oct, 2015. I had set it up the same way as in the videos in this thread.
After a initial setup problem, the system had been running efficiently since last october. One cycle went on for approx 25+ days running at 1 bubble per 8-9 secs at about 25 to 35psi.
Its 3:38 in the morning..woke up to a rigorous fizzing sound... apparently the connecting pipe of the citric acid bottle to the soda bottle had thread like tears(due to 4 months of corrosion i guess) and it was leaking. So, will replace it and the system should work fine. The other pipe parts seem to be perfectly fine. No other leakage...valve control .. pressure drop problems etc.
Though it had cost me a steep initial investment of about 1400/- for the D301 model from banggood and the diffuser for about 600/- from ebay. I think it was worth it since i did not face any hassles after the initial setup problem and it will be giving me even more service ahead.
Initial setup problem - was that the pipe which was bringing in the citric acid sol. into the soda bottle should not be dipping into the soda sol. at any point of time( everyone seems to be aware of it and its evident in the diagrams found in this thread). Otherwise it causes pressure imbalance and the whole citric sol. flows into the soda bottle and the psi goes crazy.
~ life is what you make it...