BT5 has, for me, been a bit of a pain compared to BT4 R1. I'm not going to document every issue, but these two are starting to grate my nerves:
1) For some reason BT5 can't decide if my adapter (rtl8187) should be wlan0 or wlan1. There is no wlan0, but for some reason it now uses wlan1. It's a pain if you have a bunch of scripts and aliases which used to work with wlan0, plus I have to look it up every time I plug it in (which is *frequently*).
2) I don't know if this was due to me being incredibly lucky, but I never had to airmon-ng stop my USB wifi adapter when I plugged it in. I could run airodump-ng to monitor or iwconfig to manage, but now something is putting it in some default mode. It's a pain because when switching modes it was far easier to replug the device, killing my air* processes and so forth.
I also find BT5 to be a lot less stable than BT4. In fact, I don't ever recall BT4 R1 locking up on me, but this has happened several times with BT5.