This week at work I have to deal with a couple of physical connections that were new for me. I am more familiar with LC connector and MTP is still something I am dealing with. So I learned about BiDir optics (LC) something never heard about it and the difference with SR4 optics (MTP). The vantage of using BiDir is that you can keep your current fiber install in place and upgrade from 10G to 40G without extra cost. But with SR4 you need to deploy MTP/MTO cabling although you can do breakouts (40G to4x10G or 100G to 4x25G). This is the blog entry I found quite useful for comparing both types. And this one just for BiDir.
As well, somewhere I read (can’t find the link), SR4 are more common than BiDir because is BiDir is proprietary so it has compatibility issues