I have the AM1000, and while its ok, it has its issues:
1. Its designed actually for fairly low rate filters, and comes with 12mm hose connections. Perversely most users fit it to larger tanks with more powerful filters. This causes problems as these usually have 16mm hoses so your hoses dont fit well (needs jubilee clips and still at risk of leaking) and you lose huge flow. Also if you run high flow through the unit CO2 bubbles will be entrained into the outlet flow. This means you have to fit it with media which further reduces flow. So in other words, if you have 12mm hoses its probably fine (but maybe overspecified), if you have 16mm hoses its a huge compromise.
2. Its unwieldy, and the instructions for fitting into a cabinet are poor. Frankly I couldnt work it out and I'm a qualified engineer.
3. Accessing the interior is a pain - the hex shaped inlets are too big for an easy spanner but tend to seize up and are very hard to open. Plus the top one is totally impeded by the CO2 inlet and gas bleed.
4. the CO2 inlet pipe has no valve, so you have to fit your own. Small thing but at this price not good.
5. Its expensive.
6. That said, it will dissolve a lot of gas if you don't mind the flow reduction, and the painful maintenance. I installed Eheim double taps at high cost and it was worth it otherwise this is a pain to manage.
As an alternative, look at this german website. Look using google chrome and it will offer to translate mostly ok for you. They have one with a bypass which is the one to go for if your filter is powerful. It looks like a better design all round, albeit for more money. I add that I have no experience of this in use, but on the face of it it has attractive features. And they do one that's smaller and cheaper for less money.
http://www.aquamas.de/products/CO2-...reaktor-mit-Bypass-bis-ca-3000L-komplett.html