I can only comment on AquaticMagic from 2 years ago. They were easy to deal with but shipping took a long time. At that point, they only had an eBay store, I just looked them up and now they seem to have an online store.
As for the products you are looking at....
I don't know enough about the diffusers to give advice. I think the nano one is really only good for about 10 gallons. It was very popular for DIY co2, not sure if it still is. Without knowing for sure, I think the Rhinox 2000 is the size you likely want. I believe that GLA sold the same ones for a bit more and I think that is the same I have which I have used on 29/20 longs. Can't say for certain but looks exactly the same.
As for lily pipes/tubing. 12/16mm means that the inside of your tubing is 12mm. The outside is 16mm. That means you need something around 12mm. I am 99% certain you need the 13mm ones. I hope someone else chimes in because I would hate to be wrong. The 16mm ones are way too big, assuming I am correct. 13mm may seem to big but think of 1mm, not a big deal.