I've just been researching these TVs. Although it's a bit late for the OP, I'm posting what I found out in case someone has the same question in future.
The UE32M5500 / UE32M5520 were both introduced in 2017 (the 5520 after the 5500), and appear outwardly the same. Both are Dark Titan colour, i.e. grey. There are also equivalent models UE32M5600 / UE32M5620, in silver.
The UE32M5500 / UE32M5600 feature Bluetooth audio, support for Bluetooth HID devices (keyboard, mouse, etc.), a second remote, the Samsung Smart Control, which lets you control functions for several other devices, support for the One app that manages the second remote, and finally, MBR support for viewing/recording programmes on MBR formatted external devices.
The UE32M5520 / UE32M5620 omit the above features, i.e. no Bluetooth, no second Smart remote, no MBR support (viewing/recording to external devices is possible, just not to MBR formatted ones).
Finally, Samsung's paid VOD offering TV Plus: Samsung's website says the UE32M5500 / UE32M5600 do not have TV Plus, but the UE32M5520 / UE32M5620 do. However, every retailer I checked listed TV Plus as a feature on the UE32M5500 / UE32M5600; my guess is that even if it wasn't present when the model launched, it's available as an update / app now. So I would say no difference here, although if TV Plus is a deal breaker and you're considering the UE32M5500 / UE32M5600, you may want to double check with the retailer before buying.