Thank you very much for yours answers. Very clear.
Personally, I don’t use any warnings from Ipad apps (they are mostly just distracting and not useful), but yes, occasional telephone calls when on the ground with the engine running was also my main thought (even though these also “work” with the phone stuck under the ear cushions…)
Re music: German low-level enroute ATC frequencies are often very quiet (no uncontrolled VFR traffic / FIS there). Hence, listening to music works quite nicely. (I do have a separate audio jack in the centre console of the SR22, so don’t really NEED the BT for that either).
I have a pair of BT lightspeed Zulus. I never thought I would use that feature, but actually, every other long flight I have made since having them it has been a bonus being able to call ahead while in the air or on the ground for some reason to do with the flight at hand. Previously we would have been waiting about at destination, shutting down/taxiing back etc. Much easier if your GF/Wife/Partner/Buddy can deal with the connecting bit if you dont sync before flight though!!
Regards, SD..
Two contrarian comments:
a) you can connect the phone via a cable when you need it and not have it distract you when you do not;
b) bluetooth enabled audio panels usually interface better than just the headset alone. I know b) doesn’t help when you fly different planes and/or when your plane doesn’t have a bt panel, but putting it out there nevertheless.
No comment on the BT, but why LEMO plugs? It limits you to LEMO equipped airplanes, unless you buy the expensive adapter.
I’ve the bluetooth A20’s I do use the bluetooth to make calls occasionally. It can be handy to let someone know when you’re inbound to their field and to pop the kettle on / fire up the bbq.
Sorry if I am late to the party, but I have the Lightspeed Zulu with Bluetooth Music+Phone since I was a student. The first time I used it was when I couldn‘t manage to restart a warm engine on a solo and I didn‘t want to drain the battery, hence I called my FI on the mobile, while a B350 was starting up its engines next to me and communication was crystal clear. I used it to communicate with people on the ground while organizing photo ops. In the US it was great to get your IFR clearance on remote fields, a lot of them have dedicated phone numbers published in ForeFlight. While on a cross country connecting music to the Intercom is nice, the connection to the headset is great if you do not want to disturb your partner sleeping next to you. And of course organizing changes in your hotel, restaurant or FBO reservations was great, too.
I wouldn‘t say it‘s a must have, but I would definitely buy it again.
And regarding the LEMO plugs, these are the best connectors available, it‘s a shame, that the PJ plugs are the standard. If Lightspeed would have the Bose approach, I would have gone for them. With Bose you can always have batteries in the box, but while you are on ship power, they are not drained and not damaged. If you plug in the PJ-converter, batteries are used, so it’s a seamless transition. And in newer Cirruses, you need LEMO, because there is not enough space for 5×2 PJ-plugs, so they have 5 LEMOs and only 3×2 PJ-plugs.
Bt is a plus if you run skydemon on you smart phone.you can have music, but also you can call atc in case of com failure without too much hassle.
BT is nice for getting voice alerts (eg from foreflight “rwy remaining, atis etc..”) to the headset. Edit: disregard, was already mentioned.
In the UK we call for PPR while in the air, Bluetooth is a must 
Devils advocate:
I have BT on my Lightspeed Zulu 2. I used it only once in flight, while I could hear the people on the other end crystal clear, they could not hear anything, only engine noise. On the ground there is no need to use your headset to make a phone call, just use the phone.
Also the pairing is always complicated and you can never be sure if they are connected or not.
If I could get the same headset without BT but cheaper, that would be my first choice.
