I have been waiting for this Airport Link to open for quite sometime now. It's finally been open for public trial at the beginning of this month and I just tried it out today.
It is free during this public trial period. From June to August, Monday to Friday, from 7:00-10:00 and 16:00-19:00, the train will run from Phayathai station to the airport station. It is free to use which it great :) Although the announcement said that they don't accept luggage, you can still bring your luggage in to and from the airport.
It was hassle free to get it and out. Although I find that the train seems rather narrow compare to the other trains car like the BTS and the MRT lines here. The Phayathai station also have an extension that goes toward the BTS Phayathai station. So it is highly likely that the station will be connected in the near future. It would be really troubling if the station did not have adequate escalator or lifts to help travelers with big luggage.
To avoid any complication, I think I will forgo using it on my way to Germany but I will try to make it on my return trip. I am not sure if I will be able to make it to the last train or not... But I will certainly try.