I often hear, "You should only pick your wedding photographer if they use a particular brand of camera/lens." (Usually Nikon or Canon.)
In March 2014, I was introduced to the Olympus OM-D-EM micro four thirds (M4/3rds) camera system, smaller and lighter than my Canon kit but with equally good image quality when using professional lenses from the likes of Olympus, Sigma and Panasonic. According to Olympus, the EM1 model at the time was designed to out perform the DSLR and is splashproof, dust proof but unlike the Canon system I was using, freeze proof down to minus 10!
I dipped my toe into the system but kept my Canon kit at the same time. However, in November 2016, I finally took the plunge and now exclusively use the M4/3rds system and I now use an Olympus OM-D-EM1 as my main camera. The lens I use with this camera is a Lumix 12-35mm with a fast aperture to enable me to make the subject "pop out" from the background - this is known as bokeh, a Japanese word meaning out of focus. I use an Olympus OM-D-EM5 and Lumix 35-100 with a fast aperture as my second camera and also carry back up kit in the form of lens, batteries, memory cards etc., something your "friend" or "friend of a friend" may not have.
So if my images have a "blurry background" this is done entirely for artistic reasons such as the image of the bride and groom. The same goes if I cut heads off, this is to emphasise a particular detail such as the bouquet shot below.
The EM1, EM5 and the two lenses I use are weather sealed as is my spare lens so I can carry on shooting if it's raining or snowing when your "friend" or "friend of a friend" with the cheap camera/lens, will be running for cover!
More and more wedding photographers are turning to the M4/3rd system along with other mirrorless brands such as Fuji and Sony so don't be put off by photographers using these systems as they are as good at producing quality images as the one's using the likes of Nikon or Canon.
Another plus for me, on the weight side, after a long day shooting with my Canon kit, I would be full of aches and pains the next day. Now, I don't have problems of that nature after a wedding shoot as the M4/3rds system is just so light!