Fine for the older decoders up to and including the decoder before the SD PVR, BUT after that very difficult if not impossible to get the decoders to properly receive FTA channels.
Rather, if you are keen on this, buy a dedicated universal decoder and use that to receive FTA channels.
All you need is a separate feed from an LNB for this purpose. A spare port on a 2x 4 MS will work under some conditions, provided, the FTA channels are on LO -band transponders. If they are on HI-band transponders, you will require another LNB port, which may mean getting a different LNB.
"Bandwidth, or more accurate, Data Rate, is a commodity, not a value added service"
Easyview, UEC 4T HD PVR, SD PVR, XV
Spare decoders: SD PVR, PACE HD PVR 4T, DSD 660