It works fine. Just the same as the original reader. The only difference is the new reader only supports Libre 2 sensors, is a different colour (dark blue), supports alarms (until they get stolen by an unsupported phone app), and needs charging much more often (even if you explicitly turn off the alarms).
Just to follow up on this. The new sensor (and mk2 reader) arrived yesterday so I applied it and started it with the new reader. Foolishly I did this after supper, i.e. quite late in the day. XDrip+ was then not very interested at all. XDrip+ could see the sensor, and I think it had a Bluetooth connection, but there was a problem in that OOP2 wasn't responding. There was no change in the setup between changing sensors, so I assume it must be to do with the sensor.
I spent about 3h trying different things, with the support of one of the devs on the OOP2 gitter channel too. I tried the following: uninstall & reinstall OOP2, restarting phone and apps lots of times, downgrading and upgrading XDrip+, restarting the sensor (in XDrip+), using miaomiao instead of sensor Bluetooth.
From the log messages is looked like data was being read from the sensor and being passed to OOP2, but that it was either not getting there or not getting a response (which made XDrip+ think OOP2 wasn't present.) The latter is my supposition as it had been working 5 min before with the previous sensor. I expected MM2 to work, but I think it probably also uses OOP2 to transform the data (certainly it also complained about it being "missing").
So, at about 1 in the morning, being quite tired, I installed Juggluco, set it to share data as Libre (Patched), set XDrip+ to use Libre (Patched) as its data source, and finally went to bed with a working system (to be woken up some hours later by a very shrill alarm coming from Juggluco telling me I was low, which I wasn't of course).
tl;dr - YMMV starting sensors for use with XDrip+/OOP2 with the new reader, please let me know if it does work for you. If it doesn't, the setup with Juggluco supplying data works fine, and you get more detail on the screen with the once per minute streaming (XDrip+ by default only uses/displays the 5min data)
P.S. It's not a bad thing, I was thinking that using e.g. Juggluco as the CGM provider would be a good thing as I'd like to put together an integrated app to handle food/meal tracking, have a plugin based calibration system to allow people to try different calibration approaches, and also a plugin based prediction system to again let people try different forward prediction approaches (e.g. using GI if you want, etc., etc.) I know it's yet another app, but the XDrip+ code is very complex as it's been added to over the years.