Possibly a silly question, but do you need an ADSL filter for FTTC if only the Openreach modem/router is to be installed to the phone line (i.e. no extensions, no phones or Sky boxes, just the router). In this case does a filter help/hinder or make no difference to line connection stats? I want to get the most out of my connection and will do which ever gets me the fastest and most stable connection.
I don't know about silly, it's definitely an interesting question.
Theoretically the filter only filters the phone output. However it will also present an impedance to the DSL input. Is this useful in terminating the line from the exchange/cabinet? I have no idea but suspect that results would depend on the length/impedance of the telephone line.
Why don't you try both and let us know how you get on? If you are going to fit a filter I would go for a filtered faceplate.