First big question is are all three of these of the approved list from your ISP. The ISP manages and does stuff like firmware updates on devices like these in most cases. They will only allow devices they can support to be activated on their network. Be very careful where you buy devices like this from there are model that have the same name but have different optic modules in them.
In general it won't matter these are extremely simplistic boxes. All they do is convert the gpon (ie fiber) to copper ethernet. Even on models that you have some access to there is not much you can change. They have a serial number and password that you must get from the ISP if it is not already set by the ISP.
You will need a router...