Adsl filters are there so you can use a phone on a broadband activated phone-line. They split the line with one phone line output and the other for a broadband cable should you want to plug a router into. This one by Belkin is well made and came well packaged. I like the fact it has a short cable extension meaning I can push my desk closer to the wall. Also be aware that regarding filters cheap ones are cheap for a reason. I bought a cheap unbranded one through eBay once and needless to say the phone line quality was shocking and I realised why when I opened it up and the wires were cheap and the connectors were of poor quality so it pays to invest in and this one by Belkin seems to be just that.
Pros: good quality and well made, useful cable length.
Cons: I fail to see any to be honest.
VERDICT: If you need spares or replacement filters then I can recommend these to you, self explanatory how to use them, be wary of cheap knock offs or copycat products... These are official Belkin ones and they work well