Yep I used them for years, only switched to an inline diffuser so get more kit out of the tank. I was running a nano diffuser on my 250lt as well, so that one should be fine. I would suggest getting two so you can clean one whilst the other is in the tank (they are also very easy to break!)
Its a free country, buy from who you want to! :lol: But you do get what you pay for.
Tropica spend a lot of money looking for new plants and bring 5-6 (if not more) new plants to the hobby every year. Books take years to write and publish so will never be fully up-to-date on all the latest...