This item does exactly what it says on the tin. I purchased two; one to use for an internal link in an MC220L (which is cheap and simple), and one to connect to Fiber7 (which I purchased in a kit with the media converter and a fiber... actually two since you can separate the pair).
Normally fiber is run in pairs (TX and RX), but this means you need twice as much fiber, and (in my case), you might have difficulty pulling it through small ducts like those used in Switzerland for telephone lines. BX SFPs use different wavelengths for TX and RX, so you need a different type of transceiver (A and B) at each end for it to work.
Note that the A type transceiver is typically used by ISPs like Fiber7, while the B type is for their customers to connect to the network. Also note that this worked nicely in my Cisco SG300-10 switch, while the Cisco SFP did not (and was far more expensive!).…più