I am with @keftaparty on this fiber is hard, it is fragile and you cannot fix it. everyone avoids it until they have to (meaning going over 200m). As for the and and B modes of SDI don't worry, a lot of gear is swichable, and this only applies to 3G rates, ie 1080i 50 or 1080p 25 does not have this problem.
As well there is a lot of gear that has SDI ins and outs, nothing really has fiber except for convertors. SDI-> HDMI and HDMI -> SDI are very useful tools to have around.
Personally I stay away from the cat5 or cat6 stuff as there is no real standard, mostly it is consumer gear and the results can be OK, but in my experience not reliable- it is sending a compresses signal and it changes the picture.
TBH the fiber extender looks a little cheap and dodgy, not pro gear. If price is really the problem, I have a ton of SDI to HDMI and HDMI to SDI I get from ebay for about 35 bucks each. They work fine and have not let me down. Try some cheap cable and see how far you get, you can use the €2/ meter stuff. I have some expensive belden cable I made with neutrick connectors 5 years ago, I got 200m of cable and made a lot of different lengths. They are used heaving and dragged around behind cameras show after show, and I have replace some of the tips once in this time. This is an advantage of the more expensive cable, the cheaper stuff will work but needs more care.