Well I haven't heard anything back from the German website about the "plug and play" HMF unfortunately. (It's all in German with limited translation by Google translate - have tried translating individual words and made a bit more sense of it, but I'm reluctant to order in German. Who knows what I might be ordering!)
Not sure where to go from here. My betta has now managed to shred the end of his dorsal fin presumably on the filter in the 60L altho there is some wood in there which may be a bit rough round the edges (let's face it - no wood is perfectly smooth is it?)
Looks like I'm going to have to put the stocking over the inlet grill until I can work out the way forward.