It helps if you put your general location in your profile as choices can differ a lot depending on where you live.
IMHO, the BMW unit is a bit spendy. Regardless of where you live, there are choices. Things to consider are where you can mount it, whether it is going to be outside or inside, the length of the cable, how much power you can provide, and how fast do you want to be able to charge your vehicle. Depending on where you live, there are differences in the maximum the i3 can use (doesn't mean you can't use a larger unit - still works fine, but won't charge any faster than the i3 can handle). Another thing that may be useful to you is having remote monitoring or programming of the EVSE. Some can be monitored via WiFi and some also have some programmability regarding start/stop times along with setting the maximum charge rate.
Last, and maybe most important to some, would be what, if any, rebates and inducements may be available from your utility company or government.